For indispensable reporting on the coronavirus crisis, the election, and more, subscribe to the Mother Jones Daily newsletter.

Days after threatening House Democrats who plan to investigate his administration, Donald Trump leveled a new, baseless claim against his rivals in Congress.

The prospect of Presidential Harassment by the Dems is causing the Stock Market big headaches! — Donald J. Trump (@realDonaldTrump) November 12, 2018

While the Dow Jones Industrial Average did drop more than 400 points as of 11:40 a.m. on Monday, analysts pointed not to politics, but the technology supply firm Lumentum Holdings Inc., whose stock plunged by more than 25 percent after revising its second-quarter revenue estimates downward. Apple, which is Lumentum’s largest client, also saw the value of its stock tumble on Monday.

Experts have blamed recent market volatility more on Trump’s own economic policies than the prospect of Democratic oversight. His trade wars with China and with traditional allies such as Canada and Mexico have rattled investors while the result of the midterm elections, which handed the House to Democrats and firmed up Republican control of the Senate, aligned with nearly all major predictions from pollsters.

The president’s Monday-morning tweet baffled some market observers and journalists, including Business Insider co-founder Henry Blodget and Washington Post reporter Dave Weigel.

No, Mr. President. What is causing the stock market "headaches" is rising interest rates, rising recession risk, your ballooning deficit, your trade war, and the end of your tax-cut crack hit. https://t.co/M6HJuGE1lw — Henry Blodget (@hblodget) November 12, 2018

FWIW, the DJI rose by 20% between the House's first vote to impeach Clinton (10/8/98) and his Senate acquittal (2/12/99).https://t.co/pQNSpn3TxO — Dave Weigel (@daveweigel) November 12, 2018

Fact-free attacks on the newly empowered House Democrats have been part of Trump’s standard operating procedure for the past week. A day after the midterms, he threatened to retaliate against Democrats by investigating them in the Senate. “Two can play that game!” he tweeted. During a press conference later that day, he spoke of adopting a “warlike posture” if Democrats target his family and personal business dealings.

In using the phrase “presidential harassment,” he appears to be drawing from the playbook of Senate Majority Leader Mitch McConnell, who used that phrase to warn Democrats that a strategy of intensively investigating the White House could backfire. Rep. Adam Schiff (D-Calif.), the presumptive chair of the House Intelligence Committee, has said his panel will focus their attention next year on Trump’s alleged ties to Russian money laundering and his attacks on media outlets such as the Washington Post and CNN. Acquiring Trump’s tax returns is another top Democratic priority.