Former Democratic U.S. senator and vice presidential nominee Joe Lieberman announced Wednesday that he’s endorsing his former colleague, Republican U.S. Sen. Susan Collins, in her re-election bid.

Lieberman, now an independent, also will be featured in an advertisement paid for by the Republican Jewish Coalition, NBC News reported Wednesday.

“I’m a lifelong Democrat but I put my country first, always. That’s why I’m supporting Susan Collins for Senate,” he says in the ad, referring to Collins as “a fighter for women’s issues.”

Lieberman was a Democratic senator from Connecticut for three terms – and ran as Al Gore’s running mate in 2000 – but unenrolled after he lost a 2006 primary. He then ran as an independent and won a 4th Senate term before retiring in 2012.

Collins has always touted her Senate relationships, so the endorsement isn’t a huge surprise. Lieberman endorsed Republican John McCain for president in 2008.

But the message from Lieberman reflected Collins’ waning popularity among women voters, particular since her high-profile support of U.S. Supreme Court Justice Brett Kavanaugh, whom many women opposed because of his position on abortion, among other things.

A poll of nearly 900 likely voters conducted between July 18-24 by Colby College found Collins’ main opponent, Democrat Sara Gideon, with a 12-point advantage among women surveyed. Collins led among men, 43 percent-41 percent, but Gideon had an overall advantage of 44 percent-39 percent, with 12 percent undecided and 6 percent saying they favored another candidate. Green independent Lisa Savage and Republican-turned-independent Max Linn also are in the race.

Among women under the age of 50, just 27 percent favored Collins, compared to 55 percent for Gideon.