For the younger folks: Kerry got some seriously badass medals for his military service in Vietnam. People who had been on the same boat as he did, but at a different time, worked with the Republican party to claim that he hadn’t really done what he did. The press ate this up, and distributed it widely, costing him public support and likely the election.
They are clutching at straws. Every step the Democrats have taken since Biden decided to withdraw from the race has tripped the Republicans out. They had no game plan for that contingency, and they are still several steps behind and frantically playing catch up. They are falling back on their old negative handbook tactics. Hopefully they don’t work. Because that Swiftboat Vets thing against John Kerry was really stupid. The only thing that was more stupid back then was that so many idiot voters believed it.
ETA: Some of these newspapers / media outlets are really freaked out, but only about Walz. They were fine when it was just Harris because she’s very moderate. Her choice of Walz (which was a smart choice because it reinvigorated liberal voters towards her) is the thing that they are stressing out over, because of the (tax) implication.