(CNN) House Speaker Nancy Pelosi would not commit on Wednesday to sending the articles of impeachment against President Donald Trump to the Republican-held Senate, a surprise move that injects new uncertainty into Congress' timeline of the President's trial in the chamber.

"That would have been our intention, but we'll see what happens over there," Pelosi said at a post-impeachment vote news conference Wednesday night when asked about sending over the articles.

Some progressives have urged Democratic leaders to withhold the articles until Senate Majority Leader Mitch McConnell, a Kentucky Republican, agrees to the parameters for the Senate trial that Democrats have called for , as well as agreeing to bring in firsthand witnesses like acting White House chief of staff Mick Mulvaney to testify.

On Thursday morning, Pelosi used her weekly news conference to express her concern over having a fair trial in the Senate, saying while the Founding Fathers had anticipated the possibility of a rogue President, "I don't think they suspected that we could have a rogue president and a rogue leader in the Senate at the same time."

"The next thing for us will be when we see the process that is set forth in the Senate, then we'll know the number of managers that we may have to go forward and who we will choose," Pelosi said. "That's what I said last night, that's what I'm saying now."

While Pelosi's comments create a new level of confusion to the impeachment procedure and timeline, it's unclear what the specific advantages there would be to withholding to the articles of impeachment from a Senate trial. Republicans argue there is no benefit in delaying something they don't want to spend time on anyway. When McConnell was asked this week about articles not being sent over, he told reporters, "I'm in no hurry."

But Pelosi's comments have also angered some Republicans in the Senate. GOP Sen. Lindsey Graham of South Carolina, said Thursday he was outraged. "What they're proposing -- to not send the articles for disposition to the Senate after being passed to the House -- is incredibly dangerous," he said.

Photos: The day Trump was impeached US President Donald Trump leaves the White House on his way to a campaign rally in Michigan on Wednesday, December 18. Hide Caption 1 of 11 Photos: The day Trump was impeached House Speaker Nancy Pelosi and Democratic leaders hold a news conference following Wednesday's votes. Hide Caption 2 of 11 Photos: The day Trump was impeached TV crews at the Capitol watch a live feed of the House votes. Hide Caption 3 of 11 Photos: The day Trump was impeached The US Capitol is seen from a crosswalk as the House of Representatives prepares to vote on impeachment. Hide Caption 4 of 11 Photos: The day Trump was impeached A view of the West Wing of the White House on Wednesday night. Hide Caption 5 of 11 Photos: The day Trump was impeached Pelosi walks from her office to the House chambers early on Wednesday. Hide Caption 6 of 11 Photos: The day Trump was impeached Patrons at the Capitol Lounge, close to the US Capitol, watch television coverage as the House prepares to vote on impeachment. Hide Caption 7 of 11 Photos: The day Trump was impeached A group of children tours the Capitol on Wednesday. Hide Caption 8 of 11 Photos: The day Trump was impeached US Rep. Mark Meadows, a Republican from North Carolina, is seen in Statuary Hall on Wednesday. Hide Caption 9 of 11 Photos: The day Trump was impeached A pro-impeachment rally is held on the Capitol grounds. Hide Caption 10 of 11 Photos: The day Trump was impeached The US Capitol on Wednesday morning. Hide Caption 11 of 11

"This is a land -- uncharted waters, constitutionally," Graham told reporters. "I just know this, that this matters to the future of the country. We cannot have a system where the House impeaches the president, tells the Senate how to conduct the trial, holds the articles of impeachment over the president's head at a time of their choosing to unleash them."

McConnell has openly sparred with his Democratic counterpart, Minority Leader Chuck Schumer of New York, over the format of the Senate trial. Earlier this week, McConnell rejected Schumer's call for four witnesses to testify. On the Senate floor Thursday morning, McConnell described Pelosi's delay in sending the articles of impeachment to the Senate as a sign that "House Democrats may be too afraid to even transmit their shoddy work product to the Senate."

'As long as it takes'

Pelosi said Wednesday night that House Democrats will make the decision "as a group" on when to send the articles to the Senate.

House Majority Whip James Clyburn said Thursday that he is in favor of withholding the articles "until we can get some assurances from (McConnell) that he is going to allow for a fair and impartial trial to take place."

Asked by CNN's John Berman on "New Day" how long he is willing to wait for that assurance, the South Carolina Democrat replied: "As long as it takes. Even if he doesn't come around to committing to a fair trial, keep those articles here."

House Judiciary Chairman Jerry Nadler, a New York Democrat whose committee authored the articles, said that they "need to be sent in due course."

When asked Thursday morning if the articles should be held forever, Nadler told CNN, "I would doubt that. Beyond that, I don't know."

Impeachment managers

The issue did not come up extensively at a closed-door caucus meeting Thursday morning among House Democrats, according to multiple attendees, and several members said they need to know the parameters of the Senate trial before picking impeachment managers for the Senate trial, because they may need different skill-sets

There are procedural concerns behind not sending the articles to the Senate on Wednesday night immediately after the vote. Among them: Democrats can't send the articles Wednesday night because the Senate would have to take it up Thursday, blocking votes on two spending packages that must pass before week's end to avoid a government shutdown.

In the coming days, the House must also name impeachment managers for the Senate's trial, another step Pelosi was not ready to make Wednesday night.

"We cannot name managers until we see what the process is on the Senate side, and we hope that will be soon," Pelosi said. "So far we haven't seen anything that looks fair to us, so hopefully it will be fair."

This story has been updated with additional developments Thursday.