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WASHINGTON: Donald Trump's political future may well hinge on 2018, when he risks losing control of Congress in crucial elections that kick off the next White House battle -- likely to pit the president against both Democrats and rogue Republican challengers.
Congressional mid-terms often swing against the party in power, and tradition suggests Trump's Republicans, who control the White House, the Senate and House of Representatives, are set to suffer on November 6 when Americans head to the polls.
The president is coming off a late-2017 high, when he managed to ram his massive tax cut plan through Congress.
But nearly one year into his presidency -- he marks the anniversary of his inauguration January 20 -- Trump is entangled in an alarming face-off with North Korea, has antagonized US allies over Iran, and faces accusations of racism and hatemongering.
"Historically, this is bound to be a Democratic year," Larry Sabato, who heads the Center for Politics at University of Virginia, told AFP.
"The question is, will it be a moderately Democratic year, a substantially Democratic year, or an overwhelming Democratic year?"
Polling suggests Democrats have a strong shot at flipping the House, whose 435 members serve two-year terms, in November. The prospects are slimmer in the Senate, where Democrats have to defend 26 seats compared to just eight for Republicans.
"Partisan gerrymandering is probably the only thing now that's giving Republicans some hope of hanging on to the House in 2018," said political historian Allan Lichtman of American University.
Trump and his Republicans will no doubt tout their tax cut success and the generally healthy economy.
But the president's poor approval ratings and questions about his suitability for office will also fuel the campaigns -- not to mention the Russian election meddling inquiry that hangs like a sword of Damocles over the White House.
Republican Senator John Thune predicted that "hand-to-hand combat" lay ahead in the political contests.
Collectively they will serve as opening tests for Democrats, who have been emboldened by recent successes at the polls.
"It's going to be a tough environment," Republican Senator Jeff Flake, a Trump critic, told reporters.
- Forced into primaries -
After the mid-terms, Democrats would have two years to prepare their all-out effort to block the brash billionaire Trump, who will be 74 by Election Day 2020.
"If the House goes Democratic, then Trump will be able to get exactly zero passed," Sabato predicted.
A 2018 Democratic wave would not automatically signal Trump's demise. Bill Clinton and Barack Obama suffered scathing defeats in mid-term elections in 1994 and 2010; both were re-elected two years later.
But a more potentially embarrassing hurdle for Trump could emerge in the form of the primaries that determine presidential nominees.
Even with Trump in office, the Republican Party must choose its White House nominee, and with Trump's popularity below 40 percent, analysts predict a challenger will emerge.
There are precedents for such turmoil. Ronald Reagan defied Republican president Gerald Ford in 1976, winning enough primary votes to carry the suspense into that year's nominating convention.
Senator Edward Kennedy bitterly challenged Democratic incumbent Jimmy Carter in 1980, and far-right candidate Pat Buchanan opposed fellow Republican George Bush in 1988.
The lesson? Insurgents almost always fail.
"But if a president has a really serious challenge that ends up winning a quarter or a third of the delegate votes, he's probably going to lose" re-election, as Ford, Carter and Bush did, noted Sabato.
Conversely, Clinton, George W. Bush and Obama consolidated power, won their party primaries without serious challenges, and served two presidential terms.
- Who will challenge Trump? -
No Republican has yet to commit the political sin of declaring him or herself a 2020 White House rival to Trump -- but analysts expect challengers to start emerging after the mid-terms.
One likely contender is John Kasich, Ohio's moderate Republican governor who was Trump's last rival for the 2016 nomination, and has emerged as a bridge-builder in a divisive era.
Others more hostile to Trump, including Flake or Senator Ben Sasse, could embody a return to traditional conservatism, far from the fevered populism fueled by the president. But they have nothing close to his stature or notoriety.
There is also the possibility that Trump, whose campaign committee is already raising funds for 2020, could decline to seek a second term.
It would be a first since 1968, when Democrat Lyndon Johnson quit his re-election bid after poor primary showings.
Should Trump bow out, it could clear the way for a conservative ally of the president such as Senator Tom Cotton or Vice President Mike Pence.
Many Democrats are pushing to oust Trump even before 2020, citing the suspicion he colluded with Russia to sway the last election.
But absent considerably more damning evidence, even an impeachment procedure by a Democrat-led House likely would have zero chance of success in the Senate, and could backfire politically, Sabato said.
"It might restore Trump just like it did Clinton," Sabato said, referring to Republican failed attempts to oust the Democratic president in 1998.