WASHINGTON — Senator Al Franken, a Minnesota Democrat, bade farewell to Capitol Hill on Thursday with a lengthy broadside against the policies of the Trump administration and a call for politicians to commit themselves to ‘‘honesty in public discourse.’’

Franken, who will resign his seat on Jan. 2 over more than a half-dozen allegations that he touched women inappropriately, lamented what he described as the degradation of truth in the national political debate and the hyperpartisan environment this has produced.

‘‘As I leave the Senate, I have to admit that it feels like we’re losing the war for truth,’’ Franken said in his final speech on the Senate floor. ‘‘Maybe it’s already lost. If that’s what happens, then we have lost the ability to have the kinds of arguments that help build consensus.’’

Franken will be replaced by Minnesota Lieutenant Governor Tina Smith, a Democrat, who is scheduled to be sworn in Jan. 3.

As Republicans celebrated the passage of their tax plan in another part of the Capitol, Franken denounced the bill as a means of ‘‘showering corporations and wealthy donors with tax breaks and special favors.’’

Franken is one of seven lawmakers who have resigned or decided not to run for reelection over allegations of sexual misconduct or harassment in the past three months.

In recent days, at least two of Franken’s Democratic colleagues — Senators Joe Manchin III of West Virginia and Patrick Leahy of Vermont — had said that he should withdraw his resignation to wait for the result of an ethics investigation into his behavior. In Minnesota, former governor Arne Carlson, a Republican, said the same, arguing that Franken was the victim of a ‘‘rush to judgment.’’

On Thursday, Franken’s speech was followed by warm tributes from colleagues who praised his legacy and said they were sad to see him go.

‘‘I’m sorry that he’s leaving under these circumstances,’’ Senate minority whip Richard J. Durbin, an Illinois Democrat, said. ‘‘Everyone who has ever lived has had moments they wish they could erase . . . We all draw strength from the healing power of redemption, and we can take heart in the knowledge that tomorrow is another day.’’

Franken, 65, joined the Senate in July 2009 and worked hard to distance himself from his prior career as a comedian. Cultivating a reputation as a serious legislator, he emerged as a powerful voice against corporate interests in politics and one of the Democrats’ most pointed and effective critics of Trump.

The two-term senator had risen as far as to be discussed as a possible candidate for president in 2020 until a woman said last month that he had grabbed her breasts while she was sleeping and forcibly kissed her in 2006.

That woman, Leeann Tweeden, was followed by many others who alleged sexual misconduct by Franken.

In his remarks Thursday, Franken did not address the allegations or outline his plans after leaving office.

Instead, he took a comprehensive look at his political values and how they are faring under Trump.

As Franken spoke, several Democratic colleagues sat listening. For most of the speech, there was only one Republican — Senator Lamar Alexander of Tennessee — in attendance.

Franken thanked Alexander for seeking consensus and a shared understanding of the facts as chairman of the Senate Health, Education, Labor and Pensions Committee, of which Franken is a member.