"I keep saying to people impeachment is about the truth and the Constitution and the United States. Any other issues you have with the president ... that's about the election," Pelosi said. "That has nothing to do with what is happening in terms of honoring our oath of office."
"These two are completely different," she continued. "Voters are not going to decide whether we honor our oath of office."
On Wednesday, Senate Majority Leader Mitch McConnell briefed Republican senators on the impeachment process in a closed-door meeting, suggesting a Senate trial could begin after Thanksgiving and conclude before Christmas.
"The timeline will depend on the truth-line," Pelosi said.
Pelosi, Senate Minority Leader Chuck Schumer, and House Majority Leader Steny Hoyer left the meeting after a testy exchange with the president about his plan for the region, following clashes between Turkish soldiers and Kurdish fighters in northern Syria.
The House - including two-thirds of Republicans - voted on an overwhelming bipartisan basis Wednesday to approve a resolution of disapproval of Trump's withdrawal of US troops from Syria.
Pelosi recounted her exchange with Trump at the White House, saying Trump had a "meltdown" when she and Schumer pressed him on his plan for the region.
She said Trump defended his decision to withdraw troops because of his campaign promise to bring American soldiers home.
"My question to him was, is Saudi Arabia home?" she recounted, a reference to a newly-announced deployment of troops to Saudi Arabia.
"He said, 'well the Saudi Arabians are paying for it,'" she recalled. "It just didn't add up."
She also took a moment to eulogize the late Rep. Elijah Cummings, D-Md., the chairman of the House Oversight Committee, who died early Thursday morning.
"He lived the American dream," said Pelosi, a Baltimore native, referring to Cummings as "my Baltimore brother."
Pelosi said Democrats would name their signature prescription drug pricing bill, known as House Resolution 3, after Cummings, given his focus on the issue.