WASHINGTON — A liberal activist group is ramping up pressure on Democratic congressional leaders with a new campaign to begin impeachment proceedings against President Donald Trump.

​Stand Up America, which says it has amassed 2.4 million members since former congressional candidate Sean Eldridge founded it after Trump's election, will begin pushing those members to call, confront and otherwise lobby Democratic members of the House to start the impeachment process.

The campaign kicks off on Tuesday, when the group will begin running digital ads to broadcast its message while also emailing and text messaging its members with information on how to contact their representatives.

Speaker Nancy Pelosi, D-Calif., and other party leaders have urged patience on impeachment, and ​Stand Up America, which focuses on defending the investigations into Trump and his allies, had until now echoed her call.

"When some progressives demanded impeachment after Trump fired then-FBI Director James Comey, I thought we should let special counsel (Robert) Mueller do his job first," said Eldridge, the husband of Facebook co-founder Chris Hughes.

"When Mueller's redacted report was released detailing Trump's criminal conduct, I believed Democrats in Congress should hold Watergate-style hearings to air the evidence, subpoena key witnesses and obtain Mueller's full report before considering impeachment," he continued. "I'm now convinced that it's time to stop waiting."

Pressure has been growing on Pelosi from both within and outside her caucus since the release of the Mueller report and as the White House has tried to stymie congressional investigations.

"I'm one of those who believes that we will inevitably have an impeachment proceeding, and if we don't then we've actually neglected our duty under the Constitution," Rep. John Yarmuth, D-Ky., chairman of the House Budget Committee, said on MSNBC on Saturday.

In calling for impeachment, ​Stand Up America joins other progressive groups like MoveOn and Need to Impeach, which was founded by the California billionaire Tom Steyer, who has been waging a sometimes lonely crusade on the issue for over a year, spending tens of millions of dollars of his own money to run TV ads and host events.