Walz could easily and simply shut the Republicans and his fellow vets up about this stolen valor thing.
"I had been inspired and supported by my family, friends and students to pursue a career in politics for years. This was on my mind for some time until I couldn't resist the calling any more. It's unfortunate that the optics can be seen by some that I abandoned my post years before my time out of fear of war. I promise that wasn't my intention and I apologize to my fellow vets who saw events differently than my actual intention.
As for my rank, it was simply me becoming used to being referred to by the provisional rank and habits are sometimes hard to break. I'm sorry for offending my fellow vets, most sincerely!"
But somebody coached him into acting the victim of accusations and he chose to follow their guidance. I think getting ahead of the trail with something like the example I have above would have been more effective. But I'm not into politics like that (employment) so it doesn't matter.