Sen. John Walsh (D-Mont.), recently alleged to have plagiarized his war college thesis, is dropping out of the Senate race. He was the handpicked successor to Sen. Max Baucus (D-Mont.), who received a plum ambassadorial post in China. The choice turned out to be a disaster. With Rep. Steve Daines (R) already leading by double digits, the scandal threatened to turn the race into a romp and damage down-ticket Democrats.

Sen. John Walsh, D-Mont., right, and his son Michael leave the Old Senate Chamber on Capitol Hill in Washington, after a ceremonial swearing-in ceremony with Vice President Joe Biden. (AP Photo/Lauren Victoria Burke, File)

National Republican Senatorial Committee spokesman Brad Dayspring could hardly contain his glee. He responded to the news in an e-mail blast: “After the DSCC embarrassingly put their credibility on the line with John Walsh, calling him the perfect candidate (research team, call your office) and then defending his indefensible act of plagiarism, the Senator realized that this was the end.” Privately, Republicans think Daines is one of the better GOP candidates and will defeat whomever the Dems dredge up. They aren’t saying so publicly, but the GOP seems convinced the Dems have given up on the race entirely and are simply trying to save other Democrats on the ballot.

The train wreck in Montana is symptomatic of the breakdown in vetting and candidate selection plaguing the Democrats this election. In the last two cycles, that has been a GOP handicap. This time around, the Dems have gaffe machines like Rep. Bruce Braley (D-Iowa) and candidates poorly suited to their states (e.g. Alison Lundergan Grimes’s pro-abortion stand and band of Hollywood liberal supporters are fodder for incumbent minority leader Mitch McConnell in Kentucky). Dumb errors (e.g. Michelle Nunn’s leaked strategy memo) and underwhelming candidates (e.g. Kay Hagan in North Carolina) have contributed to what seems like a perfect storm for Democrats.

The Walsh episode is a reminder that moral turpitude still can pack a punch, especially if it is not voluntarily disclosed and not atoned for. Voters can forgive infidelity, but plagiarism from a military officer is a bridge too far, at least in Montana. Candidates in both parties should be aware: If you’ve messed up, you better have already come clean. Once in full campaign mode, it’s often too late often to show remorse or to come up with a viable excuse. And if you’ve had a scandal at the state level, don’t be surprised if it comes up anew in a national race. Just because some voters back home know about your missteps doesn’t mean a national electoral or the national media does. When they find out, pleading that “this has been dealt with” isn’t going to fly. As we’ve observed, most voters have a low opinion of pols, and they tolerate a lot of very bad behavior. When it comes to out and out lying — as plagiarism is — they do holler, “Enough!”

Good riddance to Sen. Walsh. Pols, if you’ve got misdeeds in your past;, they won’t stay hidden.