CHICAGO (CBS) -- House Speaker Nancy Pelosi took a step she's been hesitant to do, formally launching impeachment proceedings against President Donald Trump Tuesday afternoon.
"I'm directing our six committees to proceed with their investigations under that umbrella of impeachment inquiry," Pelosi said.
It's only the fourth time in United States history the House of Representatives has moved to impeach the president.
The move comes after a whistleblower filed a formal complaint about President Trump's call to Ukraine's president, and allegations President Trump wanted to block that complaint to hide his push for foreign interference in next year's election.
Northeastern University political science professor William Adler said, if true, it's different than claims of Russian election interference investigated by Robert Mueller, because Trump wasn't yet the president then.
"The potential that that has occurred has really changed the politics of this quite substantially," Adler said.
The White House now says it will release the whistleblower's complaint by Thursday's deadline, as the president blasts the day's developments.
"Look, it's just a continuation of the witch hunt. It's the worst witch hunt in political history," President Trump said.
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The impeachment process begins with the House investigation. Adler says if impeachable evidence exists, it would go to the full House for a vote, requiring a simple majority to pass. Then, it would go to the Senate for trial. Ultimately, the Senate would decide if the president is removed from office, but that requires a two thirds majority.
"If they do go that route, if they're serious about trying to remove him from office, they would need to make this a bipartisan effort," Adler said.
President Bill Clinton was impeached by the House but the Senate did not vote to remove him from office. President Richard Nixon resigned before the Senate could cast its vote.
But again, this is a process – in a time of toxic partisan division.
"I think in terms of the speed here, one of the ways people sometimes phrase this ... is that Nixon was supported by Republicans up until the moment he wasn't," Adler said.
Late today, the Republican controlled Senate unanimously approved a bipartisan measure calling on the administration to release a copy of the whistleblower's complaint.
President Trump is also saying he plans to release the full, un-redacted transcript of his call to Ukraine's president tomorrow -- the same day he's set to meet with him.
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