How the impeachment process works

House Democrats are charging ahead with their impeachment inquiry into abuse-of-power allegations against President TrumpDonald John TrumpComey responds to Trump with Mariah Carey gif: 'Why are you so obsessed with me?' Congress to get election security briefing next month amid Intel drama New York man accused of making death threats against Schumer, Schiff MORE, creating the very real possibility that impeachment articles could be drafted — and voted upon — before year's end.

Behind Speaker Nancy PelosiNancy PelosiCongress to get election security briefing next month amid Intel drama New York man accused of making death threats against Schumer, Schiff Twitter, Facebook split on manipulated Bloomberg video MORE (D-Calif.), Democrats have latched on to the recent revelation, brought to light by an anonymous whistleblower complaint, that Trump had threatened to withhold U.S. military aid to Ukraine unless the country's leaders investigated corruption allegations against former Vice President Joe BidenJoe BidenPoll: Bloomberg stalls after Vegas debate Bloomberg campaign: Vandalism at Tennessee office 'echoes language from the Sanders campaign and its supporters' Democratic strategist says Biden 'has to' get second place in Nevada MORE and his son Hunter Biden.

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The notion that Trump had pressed a foreign leader to investigate a chief political rival amid his high-stakes reelection campaign sparked an uproar within the Democratic Caucus, prompting new calls for impeachment across the party's ideological spectrum and leading Pelosi last week to endorse a formal impeachment inquiry focused on the Ukraine episode.

The House Intelligence Committee, led by Rep. Adam SchiffAdam Bennett SchiffCongress to get election security briefing next month amid Intel drama New York man accused of making death threats against Schumer, Schiff The Hill's Morning Report — Sanders, Dems zero in on Super Tuesday MORE (D-Calif.), has taken the lead.

Against that backdrop, here's how the impeachment process works.

An overview

The Constitution allows Congress to remove presidents and other “civil officers” who are found to have committed “treason, bribery, or other high crimes and misdemeanors.” The document is silent, however, on what constitutes “high crimes and misdemeanors,” lending broad discretion to would-be authors of impeachment articles, who are not limited to conduct that violates criminal statutes.

The process is a two-step dance beginning in the House, which has “sole Power of impeachment.” The passage of impeachment articles through the lower chamber essentially represents an indictment. Afterward, that indictment moves to the Senate, which acts as a jury presiding over the impeachment trial. To convict, and remove a president, requires a two-thirds majority of those present within the 100-member Senate.

Impeachment is exceedingly rare. Trump is only the fourth president in the nation's history to be subject to the process — and the first to be targeted over national security concerns. Andrew Johnson was impeached by the House in 1868, and Bill ClintonWilliam (Bill) Jefferson ClintonMeghan McCain after Gaetz says Trump should pardon Roger Stone: 'Oh come on' Enlightening the pardon power The Hill's Morning Report - Democrats duke it out during Nevada debate MORE in 1998. Neither was convicted by the Senate, and both served out their terms.

Richard Nixon, facing several impeachment charges, resigned in 1974 before the House could vote on the measures.

Launching the process

There's been plenty of dispute over when — or even whether — Democrats began the impeachment process. House Judiciary Committee Chairman Jerrold NadlerJerrold (Jerry) Lewis NadlerTrump adviser presses House investigators to make Bezos testify Nadler demands answers from Barr on 'new channel' for receiving Ukraine info from Giuliani Trump predicts Ocasio-Cortez will launch primary bid against Schumer MORE (D-N.Y.) was citing impeachment going back to July, as part of court filings designed to dislodge disputed information related to the Mueller report from an uncooperative White House.

But Pelosi, for months, had avoided the “I-word” for fear of the political harm it might do vulnerable Democrats in battleground districts. That changed Sept. 24, after details of the Ukraine affair began to surface and the Speaker endorsed a formal impeachment inquiry.

Notably, however, Democrats have not staged a floor vote to launch their inquiry — a decision breaking with both the Nixon and Clinton proceedings, when the full House first voted to direct the Judiciary Committee to begin the process. That's fueled criticisms from Trump's Republican allies that Democrats are only feigning impeachment to energize liberal voters ahead of 2020 — a characterization Pelosi and Nadler have disputed.

“There's no requirement that there be a floor vote,” Pelosi told reporters in the Capitol Wednesday.

Committee role

The Judiciary Committee has jurisdiction over impeachment, and it’s there that the process was centered in the Nixon and Clinton eras. Some Democrats have also pushed for the creation of a special committee dedicated solely to impeachment — an idea party leaders have thus far dismissed.

While the Judiciary panel has led the impeachment-related investigations into Trump for much of the year — largely revolving around former special counsel Robert MuellerRobert (Bob) Swan MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE’s probe into Russia’s 2016 election interference — Pelosi broadened the scope of the impeachment investigation last week, extending it to five other committees. Of the six panels, Intelligence is leading the charge, although the Oversight and Reform and Foreign Affairs committees are also examining parts of the Ukraine episode.

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The ongoing investigations are more reminiscent of the Nixon proceedings — which involved a months-long Judiciary investigation before impeachment articles were drafted — than the Clinton affair, when Judiciary Republicans leaned heavily on the report authored by independent counsel Ken Starr.

Pelosi has made it clear that Democrats have some investigating left to do before — or if — they draft articles.

“We have to be fair to the president and that is why this is an inquiry and not an outright impeachment,” Pelosi said Wednesday. “We have to give the president his chance to exonerate himself.”

Reporting articles

While the Intelligence panel currently has the impeachment baton, leaders of the Judiciary Committee have said the process will shift back to them, in the form of recommendations from the other panels for specific impeachment articles, which Judiciary would then draft and move to the floor.

The markup of impeachment articles follows the same protocols governing any other legislation, according to the Congressional Research Service, meaning the vote would require only a simple majority on a panel where Democrats enjoy a stark numbers advantage: 24 to 17.

House vote

Impeachment articles reported by the Judiciary Committee are considered privileged, allowing Nadler to stage a floor vote virtually at will. Democrats, in such a case, could choose to vote on the articles as a package, or divide them into separate votes, as was the case surrounding the Clinton affair.

For the House, passage of impeachment articles would require only a simple majority of the chamber. If even just one article passes, the president has been impeached.

The Senate

Any articles that pass through the House then move to the Senate, which acts as “a High Court of Impeachment,” according the Senate's official website. First, however, senators must adopt a set of rules governing the process — rules that will determine how long the trial will run, what evidence is permissible and which witnesses are allowed.

To argue their case for impeachment, House Democratic leaders would appoint a slate of “managers,” who would essentially act as prosecutors in the trial. The president would appoint a team of defense lawyers to make his case. The Senate is effectively the jury. And presiding over the process would be the chief justice of the Supreme Court, John Roberts.

There is some controversy about whether the Constitution requires the Senate to conduct such a trial. But Senate Majority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellTop GOP super PAC spent money on NC Democrat Everytown plans ad blitz on anniversary of House background check bill Kentucky state official says foreign adversaries 'routinely' scan election systems MORE (R-Ky.) erased the uncertainty on that question this week, saying he is obliged to do so.

“I would have no choice but to take it up,” McConnell told CNBC on Monday.

With Republicans controlling the upper chamber — and a two-thirds majority of those present required to convict — the threat of Trump's removal is dim, at best. Yet the vote could prove difficult for vulnerable GOP senators, caught between their allegiance to a president who remains enormously popular among Republicans, and the perils of alienating more centrist voters as they seek reelection in battleground states.