Mr Trump was asked in an interview with Fox & Friends if he believes Democrats will launch impeachment proceedings if they win the House this autumn, as many suspect.
He said: “If I ever got impeached, I think the market would crash. I think everybody would be very poor.”
Mr Trump said Americans would see economic “numbers that you wouldn’t believe in reverse”.
But he also expressed doubt that that would ever happen, saying: “I don’t know how you can impeach somebody who’s done a great job.”
His comments followed his denials of wrongdoing amid allegations that he orchestrated a campaign cover-up to buy the silence of two women who say they had affairs with him.
Mr Trump also suggested it should be illegal for people facing prosecution to co-operate with the government in exchange for a reduced sentence.
He was reacting to the guilty plea entered by his former lawyer Michael Cohen to a range of charges.
Mr Trump accused Cohen of implicating him to get a better deal with prosecutors, adding that Cohen “makes a better deal when he uses me”.
The president claimed people who decide to co-operate with the government “make up stories” and “just make up lies”.
He said: “It’s called flipping and it almost ought to be illegal,” adding “it’s not a fair thing”.
Cohen pleaded guilty on Tuesday to eight charges, including campaign finance violations that he said he carried out in co-ordination with Mr Trump.
Behind closed doors, Mr Trump expressed worry and frustration that a man intimately familiar with his political, personal and business dealings for more than a decade had turned on him.
Yet his White House signalled no clear strategy for managing the fallout.
At a White House briefing, press secretary Sarah Huckabee Sanders insisted at least seven times that Mr Trump had done nothing wrong and was not the subject of criminal charges.
She referred substantive questions to the president’s personal counsel Rudy Giuliani, who was at a golf course in Scotland.
Outside allies of the White House said they had received little guidance on how to respond to the events in their appearances on cable news.
And it was not clear the West Wing was assembling any kind of co-ordinated response.
In the interview, Mr Trump argued, incorrectly, that the hush-money payouts were not “even a campaign violation” because he subsequently reimbursed Cohen for the payments personally instead of with campaign funds.
Federal law restricts how much individuals can donate to a campaign, bars corporations from making direct contributions and requires the disclosure of transactions.
Cohen had said on Tuesday he secretly used shell companies to make payments used to silence former Playboy model Karen McDougal and adult-film actress Stormy Daniels for the purpose of influencing the 2016 election.
Mr Trump has insisted that he only found out about the payments after they were made, despite the release of a September 2016 taped conversation in which Mr Trump and Cohen can be heard discussing a deal to pay Ms McDougal for her story of a 2006 affair she says she had with Mr Trump.
The White House denied the president had lied, with Ms Sanders calling the assertion “ridiculous”, but she offered no explanation for Mr Trump’s shifting accounts.