Ahead of Tuesday nights vice presidential debate, Donald Trumps Republican presidential campaign went back to the well.

On Monday morning, the campaign held a press call with Tom Behrends, a retired command sergeant major who served in the National Guard with Minnesota Gov. Tim Walz, the Democratic nominee for vice president. Behrends has become famous in conservative circles for his attacks on Walz, whom he replaced as the units command sergeant major when Walz retired.

When the nation called, Tim Walz hung up and ran the other way, Behrends said, reiterating claims hed made in 2018 when Walz first ran for governor, in 2022 when he ran for reelection and in August, after he first accepted the vice presidential nomination. When his 500 soldiers needed him most, he deserted his post and his unit.

Allies of Walz are decidedly OK with this line of attack. Theres a group of, like, four right-wing guys who served with Walz, and every single time we run they do this, a source close to the Minnesota governor said. Obviously, it doesnt land.

Republicans reliance on recycled attacks has been part of the recipe for Walz to become the most popular member of either presidential ticket, allowing him to follow the first rule of being a vice presidential nominee: Do no harm. Though he has not fundamentally changed the election, hes becoming a reliable campaigner for the Democratic presidential nominee, Vice President Kamala Harris, especially in Wisconsin and Michigan, two states where the cultural milieu is similar to Walzs Minnesota.

He came from a humble background, Sen. Amy Klobuchar (D-Minn.) told HuffPost. I think people, once they have time to know him, have liked him, and thats because hes true to himself.

The goodwill Walz generates has helped him fend off waves of GOP attacks on his honesty. In 538s polling average , 40% of Americans have a favorable opinion of Walz while just 36% have a negative opinion heading into Tuesdays debate, when he will face off with the distinctly unpopular Sen. JD Vance (R-Ohio). Vances favorability sits at just 35%, while 46% have an unfavorable view of Trumps running mate.

Vance, an Iraq War veteran, picked up the National Guard story the day after Harris picked Walz as her running mate last month, calling it shameful Walz retired before his unit went to war. Republicans were clearly hopeful it would devastate Walz, with Trump campaign co-manager Chris LaCivita expressly comparing the attacks to the infamous Swift Boat lies he pushed against then-Sen. John Kerry (D-Mass.) in his 2004 campaign against President George W. Bush.

Vance also slammed Walz for having said once, in 2018, when he was speaking in favor of an assault weapon ban, that he carried such weapons in war. A Walz spokesperson acknowledged he misspoke; The Wall Street Journals right-wing editorial page called the entire line of criticism against Walzs military record thin gruel .

Behrends called Walz a traitor and a deserter on Monday, significantly overstating his own case against the governor.

Walz was 41 when he retired from the National Guard a year older than Vance is now and had served in the guard for 24 years. Walz retired two months before his unit received official notice it would deploy, and others who served with Walz have said he had every right to retire when he did . Army leaders could have prevented Walz from retiring if his departure would have caused too much trouble for the unit.

The few times Walz has addressed the criticism of his military service, he has avoided getting into detail and thanked Vance for his time in the Marines.

I am damn proud of my service to this country, Walz said in an August speech. And I firmly believe you should never denigrate another persons service record.

Walz has made trouble for himself by misstating details over the years, including about having carried a gun in war, in describing himself as a retired instead of former command sergeant major, and, most recently, as having twice suggested this summer that he and his wife had children thanks to in vitro fertilization rather than the less-intensive infertility treatment they used.

In its press call with Behrends on Monday, Trump campaign officials spent more time emphasizing their usual messages about inflation, immigration and crime than they did talking about the National Guard. They also sought to manage expectations about Tuesday nights debate.

Tim Walz is very good in debates. I want to repeat that: Tim Walz is very good in debates, Trump campaign spokesperson Jason Miller said. Hes been a politician for nearly 20 years. Hell be very well prepared for tomorrow night.

The Harris-Walz campaign, for its part, has downplayed the importance of the debate and talked up Vance, as Walz himself has done.

Hes a Yale Law guy. Im a public school teacher, so we know where hes at on that, Walz said on MSNBC earlier this month.

Walz has rehearsed for the debate with Transportation Secretary Pete Buttigieg standing in for Vance and wearing a cheap red tie to look the part, according to a source familiar with the preparation. Vance has practiced with Rep. Tom Emmer (R-Minn.) playing Walz.

He lies with conviction, and he has these little mannerisms where its just, Hey, Im the nice guy, but hes not nice at all, Emmer told reporters on Monday.

Republicans are still searching for new material. House Oversight Committee chair James Comer (R-Ky.), who struggled to substantiate his corruption claims against President Joe Biden, has been suggesting Walz could be an agent of the Chinese Communist Party. On Monday, Comer sent the Department of Homeland Security a subpoena requesting a non-classified, Microsoft Teams group chat among DHS employees containing information about Walzs supposed communist ties.

Comer warned in a letter to DHS that if a state governor and major political partys nominee for Vice President of the United States has been a witting or unwitting participant in the CCPs efforts to weaken our nation, this would strongly suggest that there are alarming weaknesses in the federal governments effort to defend the United States from the CCPs political warfare that must be urgently addressed.