Before and immediately after the Senate narrowly voted to confirm Brett Kavanaugh to the Supreme Court on Saturday, top Democrats vowed that they would continue to fight -- not only at the ballot box in November's midterm elections, but also through further investigations and potentially even impeachment proceedings afterwards.

On Saturday, House Minority Leader Nancy Pelosi announced she planned to file a Freedom of Information Act (FOIA) request to obtain documents related to the FBI's supplemental probe of Kavanaugh, which senators said showed no corroboration of the decades-old sexual misconduct allegations against him. FBI background checks on judicial nominees have traditionally been kept confidential so that only senators, White House officials, and certain aides can view them.

“In purposefully limiting the FBI investigation, it is clear the Republicans were not seeking the truth,” Pelosi, D-Calif., wrote in a statement. “They were seeking cover to do what they wanted to do anyway. To add insult to injury, they blocked the public’s access to the report.”

Pelosi also requested any communications from Senate Republicans to the FBI concerning the scope of the investigation. Congress is legally exempt from FOIA requirements, and it was not immediately clear to what extent the FBI would respond to Pelosi's request.

READ THE EXECUTIVE SUMMARY OF THE SECRET FBI REPORT ON KAVANAUGH: WHAT WITNESSES WERE INTERVIEWED?

Meanwhile, an online petition to impeach Kavanaugh reached more than 125,000 signatures in wake of Kavanaugh's confirmation. The petition claims as grounds for impeachment, among other grievances, that Kavanaugh lied under oath about not having "legacy" connections to Yale Law School because his grandfather attended Yale as an undergraduate.

However, Yale Law School admissions officials have said that Kavanaugh would have received no boost from his grandfather's attendance at the university as an undergraduate.

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The petition also accuses Kavanaugh of lying under oath about when he learned of Deborah Ramirez's uncorroborated allegation that he exposed himself to her at a college party. Kavanaugh testified that he had heard generally that Ramirez was asking former classmates over the summer about the party to try to find someone to support her story; his denial appeared in The New Yorker's piece describing her allegations.

"There is no room for an accused sexual predator and liar on the Supreme Court," the petition, organized by the progressive CREDO Action group, continues. "Brett Kavanaugh faces credible accusations of sexual assault and perjury and should be impeached. Initiate impeachment proceedings to remove him from the federal bench."

WATCH: PELOSI COMPARES KAVANAUGH TO PUTIN, KIM JONG UN

Republicans had warned in recent days that liberal groups would rachet up their impeachment rhetoric. "You better believe that Democrats are going to do everything in their power to impeach Kavanuagh from the Supreme Court if they take control of Congress in November," Donald Trump Jr. wrote on Twitter Friday.

Alan Dershowitz, an emeritus Harvard Law School professor, told Fox News that it would be more appropriate for the Department of Justice, not Congress, to probe any viable legal violations by Kavanaugh. Partisan impeachment proceedings, he said, "would really undercut the process of confirmation and introduce a new level of McCarthyism into the process."

Nevertheless, Democratic politicians have seemingly embraced calls to continue to go after Kavanaugh. Rep. Jerry Nadler, D-N.Y, who is poised to become the chairman of the House Judiciary Committee if Democrats prevail in the lower chamber in November, promised this weekend that the FBI's recently completed supplemental review of Kavanaugh's background wouldn't be the final word.

“The Senate having failed to do its proper constitutionally mandated job of advise and consent -- we are going to have to do something to provide a check and balance, to protect the rule of law and to protect the legitimacy of one of our most important institutions,” Nadler told The New York Times on Friday.

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“We would have to investigate any credible allegations certainly of perjury and other things that haven’t properly been looked into before," the ranking Judiciary Committee Democrat said in a separate interview.

That investigation, Democrats have said, could well lead to impeachment proceedings. Federal judges can be impeached by a simple majority of the House, but actually removing Justice Kavanaugh from the bench would then require a two-thirds vote of the Senate -- an extraordinarily unlikely scenario. No sitting U.S. Supreme Court justice has ever been removed from the bench using this mechanism.

"If we find lies about assault against women, then we should proceed to impeach," Luis Gutiérrez, D-Ill., said in an interview last week.

And far-left Rep. Ted Lieu, D-Calif., wrote on Twitter in September that Congress should being investigating to see if Kavanaugh "should be impeached" based on the "new criminal allegations by Julie Swetnick."

Swetnick's credibility has taken a beating in recent days, with one ex-boyfriend telling Fox News she "exaggerated everything" and had threatened to kill his unborn child. Another ex-boyfriend similarly cast doubt on her credibility, as reports surfaced that she had previously been sued for allegedly concocting false sexual harassment claims. Swetnick is represented by anti-Trump lawyer Michael Avenatti.

And Christine Blasey Ford, the California professor who accused Kavanaugh of sexual assault, has faced questions of her own. One of her ex-boyfriends, in a sworn declaration obtained by Fox News, directly contradicted her testimony on a variety of issues, including her experience with polygraph exams and her purported fear of enclosed spaces in the wake of her alleged assault.

Republicans have defended the supplemental FBI probe into Kavanaugh's background as fair and thorough. Senate Judiciary Committee Republicans last week released an executive summary of the FBI's report, outlining each of the witnesses who were interviewed about the decades-old, uncorroborated accounts of sexual misconduct by Kavanaugh.

The full confidential report was only available to senators on a confidential basis in a secure room of the Capitol complex. While Republicans, including key swing-vote moderates like Maine Sen. Susan Collins and Arizona Sen. Jeff Flake, said they were satisfied with the report, Democrats in the Senate were openly critical.

"The fight over Judge Kavanaugh is increasing base intensity for both parties." — Political analyst Bruce Mehlman

"Well, that report -- if that's an investigation, it's a bull---- investigation," Sen. Bob Menendez, D-N.J., told a man as he walked through the Capitol complex on Thursday. "The reality is, that was not a full and thorough investigation."

There were signs that, even though Democrats face long odds in their effort to have Kavanaugh impeached, they will be successful in rallying their base to the polls in key House races in November.

“Our guys are taking a beating,” GOP consultant Rob Simms told The Washington Examiner on Tuesday, saying that House Republican candidates are being badly outspent by well-funded Democratic groups.

A new poll from Quinnipiac University showed that 49 percent of voters preferred that the Democrats take back Congress, compared with 42 percent for Republicans.

“For the first cycle in a decade, the priority in Democratic infrastructure is to win the House,” Democratic strategist Jesse Ferguson told the Examiner. “The Trump administration is fueling the desire of Democrats to win the House so that we have at least one arm of government.”

Meanwhile, though, polls by Fox News and other organizations have shown that Republicans have also been energized by what they saw as unfair, politically motivated last-minute smears during the confirmation process. Because of the specific Senate seats up for grabs this year, Republicans are expected to see gains in the Senate from the Kavanaugh confirmation battle.

Republican voters were responding not only to Kavanaugh, but Republicans' broad success in installing conservative jurists throughout the federal system. Senate Majority Leader Mitch McConnell, R-Ky., has led a successful push to install new conservative appellate and district court nominees at a record-breaking pace this year, with several more to be appointed in the coming weeks. In the last two years, he has secured not only two solidly conservative Supreme Court justices, but also 26 federal appellate judges, all with lifetime tenure.

Still, political headwinds normally work against the party of incumbent presidents in their first midterm elections. According to an analysis by former George W. Bush administration official Bruce Mehlman, in the past 11 such midterm seasons, new presidents saw their party make net gains only once in the House, four times in the Senate and zero times in state gubernatorial contests.

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"The fight over Judge Kavanaugh is increasing base intensity for both parties, helping Democrats with white college-educated women in suburban House districts while bolstering Republicans among evangelical voters in the many rural red state Senate contests," Mehlman told Fox News. He recently authorized an analysis outlining how some other major factors, including the economy and record-high levels of spending, will impact the upcoming vote.

Voters appeared particularly energized in Missouri, which Fox News polls show is tied up at 43 percent apiece for incumbent Democratic Sen. Claire McCaskill and Republican challenger Josh Hawley. Just three weeks ago, McCaskill was up 44-41 percent. Even before Ford testified against Kavanaugh, McCaskill announced that she would not support the nominee.

That decision seems to be costing McCaskill some key support. Crucially, according to Fox News polling, among the 28 percent of voters who say they could still switch candidates, almost twice as many say McCaskill voting against Kavanaugh’s confirmation would make them less inclined to back her.

North Dakota shows an even clearer picture. Vulnerable North Dakota Democratic Sen. Heidi Heitkamp, who remains undecided on Kavanaugh, appeared to be treading carefully after McCaskill's loss of support. Fox News' polling shows Republican challenger Kevin Cramer now leading by 12 points (53-41 percent). Last month, he was up by only 4 points.