US Democrats' explosive launch of an official impeachment inquiry of Donald Trump has set off a massive political battle, raising multiple questions about the process and its consequences for the Republican's tempestuous presidency.
Will conservative Republicans turn on their man, or dig in their heels? Do Democrats relish the prospect of impeaching a president for only the third time in American history, or do they too face huge risk?
US experts are looking at what might be in store in the 400 days until the 2020 election, and who stands to benefit or suffer.
- WHAT'S THE IMPACT ON TRUMP? -
"Trump is right, an impeachment inquiry will mobilize his base," Donald Wolfensberger, director of the Congress Project at The Wilson Center, told AFP.
There is little doubt that the process will rile up his most loyal followers. His 2020 re-election campaign said as much Tuesday, warning that the impeachment effort "will only serve to embolden and energize President Trump's supporters."
But even if the bid to oust Trump stalls in the Republican-led Senate, as expected, there is presidential peril ahead.
The extremes on either side will not be swayed by the impeachment process, "but voters in the middle -- independents and more moderate voters -- could," argued John Hudak, a senior fellow on governance at the Brookings Institution think tank in Washington.
A high-profile congressional debate on the president's alleged abuses of power could influence middle-of-the-road voters who supported Trump in 2016 -- voters he can ill afford to lose, given that his margin of victory was so slight.
"If I were the president, I would be worried about this," Hudak said. "There's a real risk here that this damages him with key constituencies."
- RISKS FOR DEMOCRATS TOO? -
Democrats are by no means in the clear. Their liberal base has been clamoring for impeachment, but it could blow up in their faces, experts say.
"There's the chance that Democrats will muff their opportunity to get articles of impeachment passed, demobilizing the Democratic base," said Larry Sabato, head of the University of Virginia's Center for Politics.
Even if Trump is impeached in the House, a failure to convict by the Senate will appear to some as vindication for Trump and a sign that disgruntled Democrats were engaging in political theater.
Christopher Arterton, professor emeritus of political management at George Washington University, said that without a smoking gun in the transcript of Trump's call with Ukraine's president, or in the whistleblower complaint at the heart of new abuse-of-power allegations, those in the political center "are likely to see this as an effort by Democrats to overturn the 2016 election."
There is no "off ramp" for Democrats now, Arterton added. "If they don't hold an impeachment vote, or they hold one and can't pass it, Trump will claim total exoneration."
Democrats also face a tight timeline. Should they not proceed quickly, the issue will hang over the entire presidential campaign.
- WHAT WOULD IMPEACHMENT MEAN FOR WASHINGTON?
The short answer is, even more gridlock. Republicans and Democrats already have been at loggerheads over key issues like immigration, infrastructure and guns.
Arterton said he foresees "no real progress on festering problems" from now through the election.
Not only would a drawn out impeachment fight paralyze Washington, it would dominate much of the debate in the presidential campaign.
Democrats would be "consumed by impeachment and not able to talk about their agenda," Arterton said.
A Senate trial would bring all other legislative action to a halt, potentially for months. Bill Clinton's 1999 Senate trial after impeachment lasted more than five weeks.
The impeachment scenario "will dominate the news for the rest of this year," predicts Wolfensberger.
But in 2020 it has the potential to be relegated to a "diversionary" partisan issue, Wolfensberger said, particularly if the Senate declines to convict Trump.
BEFORE TRUMP, THREE OTHER US PRESIDENTS FACED IMPEACHMENT
Before Donald Trump, three other US presidents faced impeachment proceedings. None were ousted by impeachment, although Richard Nixon resigned rather than be impeached.
- 1868: Johnson survives by one vote -
Democrat President Andrew Johnson's push for reconstruction after the American Civil War, including by reintegrating the southern States into the Union, put him in conflict with the Congress.
Congress vetoed all his legislation including the "Black Codes" -- racist laws voted by representatives from the South.
In the impasse, Johnson fired his secretary of war, prompting Congress to launch impeachment proceedings -- the first in US history.
On February 24, 1868, the House of Representatives voted 11 articles of impeachment, notably over his attempt to replace an office holder appointed by the Senate.
But after a weeks-long trial, the Senate in May fell one vote short of the two-thirds majority required for a conviction.
Johnson stayed in office but lost his party's bid to run for the next elections, entering the Senate five years later.
- 1974: Nixon resigns before impeachment -
During Republican President Richard Nixon's 1972 campaign for reelection, burglars were sent to bug the Democratic headquarters in the Watergate building in Washington.
The operation was bungled and the burglars were caught, the scandal being revealed in investigative reporting by the Washington Post newspaper.
Nixon attempted to cover-up his involvement. But on July 24, 1974 the US Supreme Court ordered him to hand over clandestine recordings of his private Oval Office conversations which provided the proof that he and his top advisors had engaged in an elaborate cover-up of the crime.
On July 30, the House Judiciary Committee approved three impeachment articles: obstruction of justice, abuse of power and attempt to impede the impeachment process by defying committee subpoenas for evidence.
Before the articles could be considered by the House of Representatives, which would have almost certainly voted for his ouster, Nixon quit on August 9.
- 1999: Clinton acquitted -
In 1998, Democratic President Bill Clinton denied under oath a sexual affair with Monica Lewinsky, a former White House intern nearly half his age.
Lewinsky at first also denied any improper relationship but later admitted to an affair, as Clinton eventually did. It led to calls for his impeachment for lying under oath and trying to cover up the affair.
On December 12-13, 1998, the House Judiciary Committee -- voting almost exclusively along party lines -- approved four articles of impeachment: two on perjury, a third on obstruction of justice and a fourth on abuse of power.
On December 19, the House of Representatives voted for impeachment on just two articles: perjury before a grand jury and obstruction of justice.
But at the Senate vote on February 12, 1999, the 45 Democratic senators stayed united against the 55 Republicans to block a two-thirds vote for conviction.
Clinton remained in office until the end of his term in 2001.
