I'd say this will cost him his speakership by 2025, if not sooner. Washington Post:

“These are allegations of abuse of power, obstruction and corruption and warrant further investigation by the House of Representatives,” McCarthy told reporters Tuesday morning. “That’s why today I am directing our House committee to open a formal impeachment inquiry into President Joe Biden.”

McCarthy spoke for three minutes, did not take any questions and left the lectern shortly after making his remarks. McCarthy has previously said he would not launch an inquiry without a vote by the full house.

The House faces a critical Sept. 30 deadline to fund the government and avoid a shutdown. McCarthy has been trying to hang on to support for a funding bill from far-right GOP lawmakers, who have been pushing to impeach Biden.

So Kevin lied about the vote by the full house, he probably can't avoid a government shutdown, and he's still serving Trump in whatever theater Trump wants to get revenge on Democrats for 2017-2020 rather than focusing on 2024.

And he doesn't have control over the fundraising platform of the Republican Party. Because Trump does.

Bold move, Kevin. Let's see how this plays out for you.

Editor's note (Karoli Kuns): They want the subpoena power. That is what this is all about. Just like the Benghazi nonsense. As The New York Times notes, "If an impeachment inquiry were to be approved, House investigators would issue subpoenas for the bank records of Mr. Biden and his family members, according to those familiar with the plans."

UPDATE: The Biden-Harris campaign has thoughts.

“As Donald Trump ramped up his demands for a baseless impeachment inquiry, Kevin McCarthy cemented his role as the Trump campaign’s super-surrogate by turning the House of Representatives into an arm of his presidential campaign. 11 days ago, McCarthy unequivocally said he would not move forward with an impeachment inquiry without holding a vote on the House floor. What has changed since then? Several members of the Speaker’s own conference have come out and publicly panned impeachment as a political stunt, pointing out there is no evidence of wrongdoing by President Biden as Republicans litigate the same debunked conspiracy theories they’ve investigated for over four years.”

“While MAGA Republicans spend all of their time attacking President Biden and his family, the president is working every day to make life better for American families across the country. President Biden will remain focused on the issues that matter to everyday Americans—lowering costs, growing the economy, making our communities safe, and protecting Social Security and Medicare—while he tries to bring the country together, not divide us even further.”