President Trump has sparked a firestorm by accusing former President Obama of wiretapping communications in Trump Tower during the 2016 campaign without providing any evidence for his claim.

But former Obama administration officials are hitting back, saying Obama did not order any wiretap. The former Director of National Intelligence, James Clapper, said he was not aware of any foreign intelligence court order authorizing a wiretap.

The White House hasn't given any more detail about what President Trump was referring to.

Here's what we know (and what we don't) about Trump's unsubstantiated wiretapping allegations:

What Exactly Did President Trump Allege?

In a tweet early Saturday morning, the president alleged that Obama had the phones in Trump Tower wiretapped prior to Election Day.

There are three important parts of Trump's unsubstantiated wiretapping allegations: Trump asserts the alleged wiretapping of his phones as a fact that certainly occurred. There is no "if." Trump claims former President Obama personally ordered -- or was at least personally involved in -- the alleged wiretapping. Trump questioned the legality of such a move, asking "is it legal" and adding "a good lawyer could make a great case" on it.

Trump hasn't provided any more detailed information about his allegations, so it's unclear if he's referring to a foreign-intelligence court order, a criminal case wiretapping warrant, some kind of rogue extra-governmental action, something he read, saw on television or heard on the radio or none of the above.

CLAIM ONE: Trump's phones were wiretapped.

What President Trump Is Saying: Trump's series of tweets say he "just found out" about "the fact that President Obama was tapping my phones in October" -- not adding any qualifiers. Trump hasn't offered any evidence since tweeting on Saturday morning.

What the White House Is Saying: White House communications staff have struggled to defend Trump's allegations in television appearances over the last 48 hours. Press secretary Sean Spicer tweeted that Trump "is requesting ... the congressional intelligence committees ... determine whether executive branch investigative powers were abused in 2016" and wouldn't comment further. But on ABC's "This Week" on Sunday, ABC News' Martha Raddatz asked White House deputy press secretary Sarah Huckabee Sanders about the claim. “All we’re saying is let’s take a closer look. Let’s look into this. If this happened, if this is accurate, this is the biggest overreach and the biggest scandal,” Huckabee Sanders said. "If, if, if, if," Raddatz replied, pointing out Trump asserted it as a fact. "I will let the president speak for himself," Huckabee Sanders continued. "He's talking about could this have happened? Did this happen?" On "Good Morning America" this morning, Huckabee Sanders told ABC's George Stephanopoulos that Obama's administration "could have done this" and Trump is asking only "that we allow the House Intelligence Committee to do its job."

What Other Officials Are Saying: The most pointed refutation of this claim came from former Director of National Intelligence James Clapper on Sunday. Asked whether he would be aware of any wiretapping of Trump's phone or any FISA (Foreign Intelligence Surveillance Act) court order authorizing it, Clapper told NBC's "Meet the Press" he "absolutely" would "know that." Then asked whether he could confirm or deny that Trump's phones were wiretapped, Clapper said "I can deny it." He continued that "not to my knowledge" was there any FISA court order of anything at Trump Tower. A statement from former President Obama did not deny any wiretapping of Trump's phones -- only denying that the White House "ordered" it or "interfered" with any Justice Department investigation. Former Obama speechwriter Jon Favreau highlighted that distinction, tweeting "I'd be careful about reporting that Obama said there was no wiretapping. Statement just said that neither he nor the WH ordered it."

What We Don't Know: While Clapper has denied any "wiretap activity" against Trump from "the part of the National Security apparatus that I oversaw," Clapper admitted he "can't speak for other Title III authorized entities in the government or a state or local entity." Neither former President Obama nor any active Department of Justice official has unequivocally denied that there was any wiretapping at all. And because any wiretap would be protected under the highest levels of classification, it's not clear how many officials would be in a position to know about it. However, multiple former senior intelligence officials have told ABC that in almost every circumstance, President Trump would have the ability to ask and find out if he had been being wiretapped in the past. The only real circumstance in which he might not be privy were if that warrant was directly focused on him.

CLAIM TWO: Former President Obama personally ordered -- or was at least personally involved in -- the alleged wiretapping.

What President Trump Is Saying: In four separate tweets, President Trump directly ties former President Obama to the alleged wiretapping, saying "Obama had my 'wires tapped'" and "Obama was tapping my phones." President Trump hasn't offered any evidence since tweeting on Saturday morning.

What the White House Is Saying: On "Good Morning America" Monday morning, Huckabee Sanders backed off the assertion it was Obama personally, telling ABC News that "whether it was directly ordered by this president specifically, his administration could have done this." On "This Week" Sunday, Huckabee Sanders said "there certainly could have been" a FISA order that Obama did not personally order. She pointed to then-Attorney General Loretta Lynch's meeting with former President Bill Clinton on the tarmac during the investigation into Hillary Clinton's personal email server as evidence that Obama himself "got directly involved" in other investigations (both Lynch and Clinton denied discussing the email case). Huckabee Sanders continued to say that, even if Obama wasn't personally involved, it "would have fallen under this administration and this past president."

What Former President Obama Is Saying: A spokesperson for former President Obama said "no White House official ever interfered with any independent investigation led by the Department of Justice" in a statement on Saturday. "Neither President Obama nor any White House official ever ordered surveillance on any U.S. citizen. Any suggestion otherwise is simply false." The statement did not explicitly rule out that wiretapping had been initiated by the Department of Justice. Former National Security Adviser Ben Rhodes tweeted a similar sentiment to Trump: "No President can order a wiretap. Those restrictions were put in place to protect citizens from people like you."

What Other Officials Are Saying: FBI Director James Comey asked the Justice Department to publicly refute President Trump's assertion that Obama ordered a wiretap of Trump's phones prior to the election, government sources told ABC News. Comey was concerned the president's tweets -- which he believes are inaccurate -- created the impression that the FBI acted improperly, and he wanted to set the record straight, the sources said. The FBI and Department of Justice declined to comment.

What We Don't Know: While Obama has denied any order or involvement and Comey asked his superiors for a public refutation, it's not clear whether it's possible a Justice Department investigation may have existed independently of Obama's influence or whether these top officials may be choosing not to publicly confirm the existence of such a highly classified and sensitive investigation. And while former DNI Clapper has denied the existence of a FISA Court order, we don't know whether there may have been a criminal wiretap warrant outside of a foreign intelligence-related investigation or if a state or local agency was involved.

CLAIM THREE: The legality of the alleged wiretapping is questionable and "a good lawyer could make a great case."

What President Trump Is Saying: President Trump asked via Twitter: "Is it legal for a sitting President to be 'wire tapping' a race for president prior to an election?" He added that Obama was allegedly "turned down by court earlier." He compared the alleged action to "Nixon/Watergate." President Trump hasn't offered any evidence since tweeting on Saturday morning.

What the White House Is Saying: On "This Week," Huckabee Sanders told ABC News' Raddatz that if this wiretap had happened, "this would be the greatest abuse of power and overreach that's probably ever occurred in the executive branch." And Monday morning on "Good Morning America," Huckabee Sanders asserted to ABC News' Stephanopoulos more generally that "the administration was wiretapping American citizens" and "the fact that it was being done is a fact that we should be talking about." A spokesperson for former President Obama said "no President can order a wiretap." FISA courts have approved over 10,000 requests for electronic surveillance from the Justice Department since 2009.

What Other Officials Are Saying: Former Obama Senior Adviser David Axelrod tweeted: "If there were the wiretap @realDonaldTrump loudly alleges, such an extraordinary warrant would only have been OKed by a court for a reason."

What the Law Says: A wiretap order on Trump could have been legally obtained from a Foreign Intelligence Surveillance Court -- commonly referred to as a "FISA Court" -- a secret tribunal with legal authority to grant warrants for electronic surveillance against would-be spies or terrorists. The court -- made up of 11 federal judges, serving 7-year terms and selected by the chief justice of the Supreme Court -- meets in private, sometimes in the middle of the night. FISA targets are highly classified. We also know a FISA court order is not the only way to authorize a wiretap: non-intelligence, criminal wiretap warrants can be obtained, but require that the individual under surveillance is using the device in connection with a past or future crime.

What We Don't Know: While Clapper has said he's not aware of any foreign intelligence-related FISA Court order and would be aware if there was one -- and former President Obama denied personally ordering a wiretap of Trump -- we don't know whether a criminal wiretap order remains sealed or whether Trump is alleging -- like Nixon and Watergate -- some kind of extra-governmental group working illegally.