WASHINGTON (NYTIMES) - Senate Republicans rallied Tuesday (Jan 26) against trying former President Donald Trump for "incitement of insurrection" at the Capitol, with only five members of his party joining Democrats in a vote to go forward with his impeachment trial.

By a vote of 55-45, the Senate narrowly killed a Republican effort to dismiss the proceeding as unconstitutional because Mr Trump is no longer in office.

But the numbers showed that loyal Republicans are again poised to spare him from conviction, this time despite his role in stirring up a mob that violently targeted lawmakers and the vice-president on Jan 6 as Congress met to finalise the election.

"I think it's pretty obvious from the vote today that it is extraordinarily unlikely that the president will be convicted," said Senator Susan Collins of Maine, one of the five Republicans who voted to proceed to trial. "Just do the math."

It would take two-thirds of senators - 67 votes - to attain a conviction, meaning 17 Republicans would have to cross party lines to side with Democrats in finding Mr Trump guilty.

If they did, an additional vote to disqualify him from ever holding office again would take a simple majority.

Aside from Ms Collins, the only Republicans who joined Democrats in voting to reject the constitutional objection and proceed were Senators Lisa Murkowski of Alaska, Mitt Romney of Utah, Ben Sasse of Nebraska and Patrick Toomey of Pennsylvania.

All five had previously said they were open to hearing the House's impeachment case, which was adopted in a bipartisan vote a week after the attack.

With the facts of the case still spilling forth and the meat of the trial delayed for two weeks, senators could change their views.

Several Republicans who voted Tuesday to uphold the constitutional challenge, which would have effectively killed the trial, rushed afterward to clarify that they remained open-minded about the trial, which next convenes Feb 9.

It appeared that Senator Mitch McConnell of Kentucky, the Republican leader, was among those making such a calculation.

He had twice signaled in recent days - through advisers and then in a letter to colleagues - that he was open to convicting a former president he privately disdains, and he publicly asserted last week that Mr Trump had "provoked" the mob.

But if Mr McConnell was trying to soften the ground for a faction of Republicans to abandon Mr Trump and jettison him from the party, it had become increasingly clear that no such coalition was emerging.

When his fellow Kentuckian Senator Rand Paul lodged a constitutional objection to the proceeding minutes after the Senate convened as a court of impeachment, Mr McConnell voted with the vast majority of his conference in favour of the challenge.

Mr McConnell made no public comment about his views of the vote nor did he speak up on the matter during a private Republican luncheon beforehand, according to people familiar with the session.

The showdown caught many senators off guard on a day that they expected to be devoted largely to the carefully scripted ceremony and logistics of a trial.

Senator Patrick Leahy, the Senate president pro tempore, was sworn in as the presiding officer and then asked all 100 senators to take an oath to administer "impartial justice" during the trial.

Senators were warned by the sergeant-at-arms "on pain of imprisonment" to remain silent.

It was then that Mr Paul, an outspoken defender of Mr Trump, lodged his formal objection.

"Private citizens don't get impeached," Mr Paul had said a short time earlier, calling the trial "deranged" and vindictive.

"Impeachment is for removal from office, and the accused here has already left office."

Senator Chuck Schumer, the majority leader, quickly moved to shut down the request.

"The theory that the impeachment of a former official is unconstitutional is flat-out wrong by every frame of analysis," Mr Schumer said. "It has been completely debunked by constitutional scholars from all across the political spectrum."

The Senate has clearly taken that position in the past. In 1876, as the House was preparing to impeach him on corruption charges, William Belknap, Ulysses S. Grant's secretary of war, hurried to the White House, where he tendered his resignation in tears just before Congress could act.

The House proceeded anyway, and when the case arrived in the Senate, a majority of the body decided that it retained jurisdiction to hear it, notwithstanding Belknap's departure from office.

Support for a constitutional argument against holding the trial had been growing in the Senate in recent days, particularly among Republicans who showed little interest in mounting any substantive defence of Mr Trump's conduct.

But the overwhelming level of Republican support exceeded what almost anyone was expecting.

Mr Paul declared victory, saying, "Forty-five votes means the impeachment trial is dead on arrival."

Ms Murkowski, who has praised the House's move to impeach and called Mr Trump's actions "unlawful," reluctantly agreed.

She told reporters that she feared that it would be impossible for most of her Republican colleagues to truly consider supporting a conviction after they had put themselves on record arguing that the trial should not even take place.

"That's why I thought it was a little unfortunate that we had this very spontaneous vote on an extraordinarily significant matter without the considered debate and analysis," she said. "People had to make really quick decisions."

But other Republicans said their votes to uphold Mr Paul's objection should not be read as opposition to hearing the case against Mr Trump.

Senator Rob Portman of Ohio said that he voted with Mr Paul because he wanted a "fulsome discussion" on the issue of constitutionality, not necessarily to kill the trial.

"I've not made my mind up," he said. "I'm a juror."

He and Senator John Thune of South Dakota, the Republican whip, suggested Mr McConnell might feel the same way.

"I don't think it binds anybody once the trial starts," Mr Thune said.

Far from settled, the argument over constitutionality will reappear when the trial reconvenes in February, when senators may seek to use it as justification for voting to acquit.

The House managers have already begun preparing a constitutional justification for proceeding, and Mr Trump's lawyers will be asked to argue the opposite as a key plank of their defence.