The chairman of the National Republican Congressional Committee on Tuesday warned Democrats that they will lose their House majority in next year's election on an impeachment inquiry on President Donald Trump.

"For the past three years, the socialist Democrats have been obsessed with impeaching the president and backfilling in the reason after the fact," Rep. Tom Emmer, R-Minn., said in a statement.

"They have become so radicalized by their hatred of President Trump that they are willing to plunge the nation into a constitutional crisis based on secondhand gossip.

"Democrats have lost their sanity and any remaining credibility with the American people," Emmer said.

"Make no mistake about it: backing impeachment will cost the Democrats their majority in 2020."

Emmer's statement came amid reports that House Speaker Nancy Pelosi, D-Calif., is expected to announce a formal impeachment investigation against Trump.

The president tweeted Tuesday that he would release a transcript of his July 25 telephone call with Ukrainian President Volodymyr Zelensky — and Pelosi said earlier Tuesday that Trump's move would not dissuade Democrats from pursuing any investigation.

Democrats hold a 235-199 majority in the House, having flipped many Republican districts during last year's election.