WASHINGTON — A day after the House’s historic vote to impeach President Trump, uncertainty about the timing and rules of his eventual Senate trial descended over Capitol Hill.

The conventional wisdom echoed in Washington for weeks — that the GOP-controlled Senate would quickly acquit Trump after a trial beginning and ending in January — was thrown into doubt when House Speaker Nancy Pelosi on Wednesday night left open the question of when she would send the two articles of impeachment to the Senate. The San Francisco Democrat said she is looking for assurances that Republicans who control the chamber would hold a “fair trial.”

That sounded like code for Democrats’ demands that the Senate hear from current and former White House aides whom Trump barred from testifying before the House about the holdup of U.S. military aid to Ukraine while he sought Kyiv’s announcement of investigations into Democrats.

If it was, it didn’t convince Senate Majority Leader Mitch McConnell, R-Ky. He suggested from the chamber’s floor Thursday that Democrats knew they had a weak case when they impeached Trump for allegedly abusing his power and obstructing Congress’ investigation, and that “the prosecutors are getting cold feet in front of the entire country” about giving the articles to the Senate.

Pelosi responded at a news conference that a decision on “who and how many” House impeachment managers would handle a trial awaited the Senate’s setting of trial rules. She cut off questions about whether she planned to delay, lamenting, “We impeached the president — immediately, everybody was on to the next thing.”

There are two ways this could play out in the next few weeks:

Democrats could benefit: Pelosi hasn’t said she plans to hold the articles until she wins Senate Republicans’ concessions. But she hasn’t ruled out the possibility, either.

GOP lawmakers were quick to seize on Pelosi’s ambiguity. House GOP leader Kevin McCarthy of Bakersfield told reporters, “She’s admitting defeat by not sending them.”

But where Republican leaders see a bad PR move, some legal experts see a way for Democrats to keep impeachment alive while looking for additional evidence to make a more convincing case.

“I think they understand that the longer this goes on, the public learns more facts and people become more troubled,” said Jonah Gelbach, a professor at the UC Berkeley School of Law.

If Pelosi does go this route, it could lead to an unprecedented legal battle because the Constitution doesn’t stipulate that the House must forward articles of impeachment to the Senate. Impeachment rules that the Senate adopted in 1986 would prevent McConnell from calling a trial without the House articles being formally delivered, Gelbach said.

“She knows how to use the rules for maximum advantage,” he said of Pelosi.

Republicans could benefit: Any attempt to delay the Senate trial carries risks for Democrats for one clear reason: There is almost zero doubt that Trump will be acquitted, whenever the trial occurs.

That could create a perception that Democrats are delaying the inevitable to prolong whatever damage impeachment may be doing to Trump’s re-election hopes.

Senate Republicans leaders have been explicit in stating that the trial will be crafted to help Trump. “Everything I do during this, I’m coordinating with the White House counsel,” McConnell told Fox News last week.

Senators are expected to vote in early January on rules for the trial. Those rules could include whether witnesses will give testimony in person or through videotaped depositions, and even whether there will be any witnesses at all.

Bernadette Meyler, a constitutional law expert at Stanford Law School, said that given McConnell’s mind-set, Democrats might find it politically wise to end a standoff they cannot win.

“I really doubt they’ll be able to succeed in changing the procedure,” Meyler said. The longer the speaker delays in delivering the case, she said, “it starts to look like Pelosi is holding things up too much.”

Court remedy likely off table: One consequence of Wednesday’s impeachment vote is that it signals the House probably won’t be asking a court to order the Trump administration to comply with its subpoenas seeking White House witnesses and documents that the president refused to turn over.

Gelbach said while the entire scenario is largely “uncharted waters,” a judge might find the House’s demands for the testimony and records are moot now that lawmakers have already voted for impeachment.

“I would be very surprised if the House could get any traction in the courts at this stage,” he said.

Democrats decided not to seek such an order before they impeached the president, arguing among other things that the possibility that Trump was soliciting foreign interference in the 2020 election meant they couldn’t wait for a lengthy court fight.

House intelligence committee Chairman Adam Schiff, D-Burbank, who presided over impeachment hearings, said Democrats were unwilling to “wait months and months while the administration plays a game of rope-a-dope in an effort to try to stall.”

McConnell mocked that stance Thursday, saying Democrats had impeached Trump for obstructing their inquiry without waiting for the courts to decide whether they had the legal right to what they were seeking.

He said Democrats want a “pretrial guarantee of certain witnesses whom the House Democrats themselves did not bother to pursue as they assembled their case.”

Dustin Gardiner is a San Francisco Chronicle staff writer. Email: dustin.gardiner@sfchronicle.com Twitter: @dustingardiner