But he promised that Americans will soon see 'some very interesting items' that could shed light on his still-unsubstantiated claim that former President Barack Obama 'wiretapped' his phones.
Trump dangled the possibility during an interview with Fox News Channel host Tucker Carlson in Michigan, even as top congressional leaders of the Intelligence committees said they have seen no evidence to support the president's March 4 claims.
''Wiretap" covers a lot of different things,' Trump cautioned Carlson, suggesting that he might turn up evidence of other kinds of surveillance.
Asked how he concluded he was being snooped on, Trump cited a January 20 New York Times article 'where they were talking about wiretapping. There was an article, I think they used that exact term.'
'I read other things,' he told Carlson. 'I watched your friend Bret Baier the day previous where he was talking about certain very complex sets of things happening, and wiretapping.'
'I said, "Wait a minute, there's a lot of wiretapping being talked about",' Trump recalled. 'I've been seeing a lot of things.'
Trump's comments fit with a statement from White House press secretary Sean Spicer on Tuesday, suggesting that Trump will ultimately be proven correct.
'There is significant reporting about surveillance techniques that have existed throughout the 2016 election. ... I think he feels very confident that what will ultimately come of this will vindicate him,' Spicer told reporters.
The president said Wednesday that his administration 'will be submitting certain things' to congressional committees that are investigating his claim that the Obama administration conducted top-secret surveillance on him.
'And I will be perhaps speaking about this next week.'
Trump has scheduled a campaign-style rally Monday night in Kentucky.
Carlson challenged Trump, asking him why he wouldn't wait to tweet about a serious charge until he had evidence to support his statements.
'I think that frankly we have a lot right now,' Trump replied.
He added: 'I think you're going to find some very interesting items coming to the forefront over the next two weeks.'
The leading Republican and Democrat on the House Intelligence Committee said Wednesday that they have seen no evidence to support President Donald Trump's March 4 claim that the Obama administration had tapped his phones at Trump Tower during the 2016 campaign.
'To date I've seen no evidence that supports the claim that President Trump made,' said Rep. Adam Schiff, the Democrats' ranking committee member.
'Thus far we have seen no basis for that whatsoever,' he told reporters alongside fellow Californian Devin Nunes, the committee's Republican chairman.
Nunes added: 'We don't have any evidence that that took place.'
Former President Barack Obama is said to have 'rolled his eyes' when he first heard news of Trump's allegations.
Schiff said Wednesday that he and Nunes have given the Justice Department until next Monday to answer written questions about whether it had applied for warrants to surveil Trump and his associates.
'We're both willing to use compulsory process if that's necessary,' he said, referring to the subpoena power granted to Congress, 'though neither of us, I think, believe that will be necessary.'
Previous attorneys general have ignored congressional subpoenas, including Obama's DOJ chief Eric Holder – who was later held in criminal contempt of Congress for it.
FBI Director James Comey will be grilled next Monday in an Intelligence Committee hearing, the majority of which Nunes and Schiff expect they will be able to conduct in public.
'It deeply concerns me that the president would make such an accusation without basis,' Schiff said.
Nunes hinted that the Intelligence Committee could have problems establishing that because the Office of the Director of National Intelligence was reluctant to let Congress have access to its high-tech materials that could establish Trump was right.
He said it wasn't clear 'whether or not they are going to let us have the proper computer technology that we need to go through the evidence that exists out at the CIA, out at Langley, and we are trying to work through that.'
'I can tell you it has become a little bit of a stumbling block for our investigators to actually be able to compile and cull through the information.'
But Nunes said that while Trump claimed Obama personally engaged in secret surveillance, Americans would have to decide whether to season his tweets with a grain of salt.
'President Obama wouldn't physically go over and wiretap Trump Tower, so now you have to decide ... are you going to take the tweets literally, and if you are, then clearly the president was wrong,' he told reporters.
'If you're not going to take the tweets literally and there's a concern that the president has about other people, other surveillance activities looking at him or his associates either appropriately or inappropriately, we want to find that out. I think it's all in the interpretation of what you believe.'
On the other side of the Capitol, South Carolina Sen. Lindsey Graham gave Comey until a hearing this afternoon to provide proof that the DOJ obtained a warrant for the alleged Trump surveillance or declare once and for all none exists.
The FBI told his staff minutes before testimony was due to begin that it would respond to a March 8 letter Graham and Democratic Sen. Sheldon Whitehouse sent asking for information about warrants that may have been requested against Trump in a 'classified briefing.'
'Apparently the FBI has contacted my staff [and said] that they will be at some date in the future providing us an answer to this in a classified manner,' Graham stated.
Whitehouse scolded the FBI for refusing to make a public promise that it will 'get to the bottom of this.'
Using a baseball metaphor, he said, 'That is a recipe for having the ball drop between the second baseman and the short stop.
'We are entitled to investigate under the constitution. They have executive responsibilities. And if we are only connecting with one another in a classified fashion, I don't think that serves the public interest.'
This FBI's response to Graham came after he levied threats at the law enforcement agency on Tuesday night and Wednesday morning.
'Congress is going to flex its muscle here,' the Republican lawmaker warned Comey in a Wednesday morning appearance on the 'Today' show.
If the FBI official continues to dodge, Graham said he will issue his own subpoena for the information and hold up the nomination of the deputy attorney general until he gets what he wants.
'We'll issue a subpoena to get the information,' he said on Today. 'We'll hold up the deputy attorney general nomination until Congress is provided with information to finally clear the air as to whether or not there was ever a warrant issued against the Trump campaign.'
The Justice Department could not have legally surveilled Trump without a court-ordered warrant, Graham argued, and so far, he's seen no evidence that one was ever issued.
'I have no evidence of it. I'm suspicious of it, but now getting concerned because it's taking so long to answer my letter,' Graham said.
White House Press Secretary Sean Spicer declined to comment on the dispute during a question and answer session with reporters traveling on Air Force One later in the day.
'I'm not going to interfere with those discussions,' he said. 'I don’t want to get into the middle of Congress and their requests, so I'll leave that up to director Comey, and to [Congress].’