Republicans came into this election cycle licking their chops over the unique opportunity they have in the Senate, where Democrats will defend 26 seats to the GOP’s nine. Ten of those races will take place where incumbent Democrats have to defend seats in states that Donald Trump won in 2016. If the GOP picks up even half of those seats, they’ll have a firm majority for the remainder of Trump’s term.

Prospects for pickups outside those seats look grim — or do they? The New York Times sent up a warning about New Jersey, where Democrats decided to stand by Robert Menendez despite his trial and Senate Ethics probe over corruption allegations. After squeaking by an unknown primary opponent, Menendez is suddenly looking vulnerable:

In theory, Mr. Menendez, 64, should win easily: Registered Democratic voters outnumber Republicans by nearly 900,000; President Trump remains deeply unpopular; contested congressional races are energizing Democrats; and he has the backing of a Democratic machine that still has enough clout to deliver victory.

But despite the advantages, Mr. Menendez has shown signs of weakened support. In the primary, Lisa McCormick, a small-business owner and unknown candidate with virtually no money, managed to win nearly 40 percent of the vote. A significant number of voters view Mr. Menendez unfavorably, according to recent polls. Real Clear Politics, a nonpartisan polling aggregate site, downgraded Mr. Menendez’s chances from “likely Democrat” to “leans Democrat.”

His Republican opponent, Bob Hugin, 64, a wealthy former pharmaceutical executive, has already spent $15 million of his own money on the race, largely on negative attack ads. New Jersey residents tuning into the World Cup were constantly reminded of Mr. Menendez’s federal corruption trial. A recently formed separate super PAC called Integrity NJ that focuses on defeating Mr. Menendez has already raised over $2 million.

Just how much risk is there for Democrats in New Jersey? Hillary Clinton won the state 55/41 in 2016, only slightly off from Barack Obama’s 58/41 performance four years earlier. Menendez won that 2012 race 58/40 against state senator Joe Kyrillos. Without a presidential or gubernatorial race on the ticket, however, turnout and Menendez’ smelly reputation might make this at least an interesting race.

The bigger risk is the need to commit resources to defend the seat. Hugin’s self-funding, unlike Kyrillos, although other groups are coming to Hugin’s aid and the RNC is likely to turn up the volume on its efforts. Democratic committees haven’t spent much money there yet, but Menendez says that the DSCC might start contributing some resources. If so, it will necessarily shift them from resources meant to strengthen some of the red-state Democrats fighting for their political lives in places like Indiana, West Virginia, Missouri, and North Dakota, among others. The state party is now fundraising to help Menendez out, which will distract them from some of the important House races they want to support. Menendez could end up being a drain that might tilt other races outside and inside of New Jersey besides his own.

If so, Democrats deserve what they get for continuing to support Menendez. His corruption trial ended with a hung jury largely because prosecutors couldn’t quite meet the McDonnell bar in proving quid pro quo, but the favors that flowed back and forth between Menendez and Medicare scam artist Salomon Melgen was bad enough to warrant expulsion from the Senate. Instead of looking for a new candidate with a better handle on ethics, Democrats doubled down on Menendez. He’ll probably survive in the election, but a loss would serve Democrats right.