Former senator John Warner (R) announces his support for Hillary Clinton and Tim Kaine for president and vice-president in September 2016. (Jahi Chikwendiu/The Washington Post)

Former senator John W. Warner, a dean of Virginia’s Republican Party, said Wednesday that he will cross party lines to support Sen. Tim Kaine in his reelection campaign.

The endorsement, announced by the Democrat’s campaign, underscores the deep ambivalence Virginia Republicans feel over Corey A. Stewart, an acolyte of President Trump who is their party’s nominee in the Nov. 6 election.

Stewart, who last year championed efforts to preserve Confederate monuments in Virginia, has battled controversy over ties to white supremacists, leading other Republicans to steer clear of his campaign.

In a statement, Warner, 91, cited Kaine’s leadership on the Senate Armed Services Committee as one of the reasons for supporting the Democrat. He also referred to the deep partisanship in Washington under Trump.

“Tim’s unquestioned integrity and moral character are sorely needed in the Senate at this most unusual time in our nation’s history,” said Warner, who also endorsed Hillary Clinton over Trump in the 2016 presidential election.

During Kaine’s first run for the U.S. Senate in 2012, Warner endorsed his Republican opponent, George Allen. And before that, when Kaine ran for governor in 2005, Warner endorsed his Republican opponent, Jerry Kilgore, serving as honorary co-chair of Kilgore’s campaign.

But in 2016, Warner cast his first vote for a Democrat in a presidential race, when he voted for Clinton and her running mate, Kaine, against Donald Trump and Mike Pence.

A recent poll by the University of Mary Washington in Fredericksburg showed Kaine leading the race by nearly 20 points. The poll also showed that 73 percent of Republican respondents supported Stewart, while 15 percent of Republicans surveyed said they’d vote for Kaine.

Stewart dismissed the Warner endorsement.

“Retired king of the establishment,” he said, in a text. “LOL.”