Having defied the Republican establishment to win first a presidential nomination and then the Oval Office, US President Donald Trump has been the dominant partner in what has been little more than a marriage of convenience.
However, Mr Trump’s abrupt decision to pull troops out of north-east Syria has put this co-dependent relationship under strain.
Normally loyal Republicans, who backed Mr Trump on a range of issues from gun control to his ill-judged attempt to persuade Ukraine to dig dirt on former vice president Joe Biden, have broken ranks.
They reacted furiously to a decision that looks likely to leave the Kurds, who fought alongside US troops in the battle against ISIS, at the mercy of Turkish President Recep Tayyip Erdogan.
These are the same Trump supporters, such as Republican Senate leader Mitch McConnell, who have been content to dismiss the Ukraine scandal as a Democrat put-up job.
"A precipitous withdrawal of US forces from Syria would only benefit Russia, Iran and the [President Bashar Al] Assad regime," he said. "And it would increase the risk that ISIS and other terrorist groups regroup." Mr McConnell has not been the only ally to desert the president.
Nikki Haley, the former UN ambassador who has been tipped as a possible running mate for Mr Trump, tweeted: “We must always have the backs of our allies if we expect them to have our back.”
Mike Rogers, the former Republican chairman of the House Intelligence Committee, asked: “Who would trust us? Who would say we are willing to take a chance on the United States?”
Lindsey Graham, a foreign policy hawk and normally an ally of Mr Trump, described the move as dangerous. "President Trump may be tired of fighting radical Islam. They are NOT tired of fighting us," he tweeted.
They lined up alongside Republicans who traditionally have not been afraid to speak up against Mr Trump, such as Marco Rubio – who described the move as a “grave mistake” – and Mitt Romney, who called the decision a betrayal.
"I think there are a number of Republicans who have been discontented over Ukraine but have been reluctant to come forward," said David Gergen, a political commentator who served as an adviser in the administrations of Richard Nixon, Gerald Ford, Ronald Reagan and Bill Clinton.
"I think their frustration levels have been rising, and this decision may well become a tipping point," he said.
“They are unhappy at what seems an impulsive decision. Many made pledges that they would support the Kurds.
“I would not be surprised if he backtracks on some of this, rather than let Erdogan commit genocide. He can’t start bombing if there are US troops on the ground and we may see some remaining, sprinkled among the Kurds.”
Underpinning the row is a long-standing difference of approach to foreign policy between Mr Trump and traditional Republicans.
The GOP has regarded itself as the party of national security, supporting the use of force to protect the country's global interests.
Mr Trump, who has rattled through three national security advisers, has taken a different view of what he describes as American interests.
He has long sought to disentangle the US from acting as what he describes as “the world’s policeman”.
It is a view shared by a handful of Republicans on Capitol Hill, notably Kentucky Senator Rand Paul. He, at least, threw his support behind the decision, tweeting: "I stand with @realDonaldTrump today as he once again fulfils his promises to stop our endless wars and have a true America First foreign policy."
But Mr Paul is in the minority.
The big question is whether the row over Syria has raised the spectre of divorce in the Republican Party at a time when the Democrats are pushing for impeachment.
At the very least a prolonged period of marriage counselling may be a judicious move.