WASHINGTON -- In a year in which six vulnerable Senate Democrats will be running in states won by Donald Trump, the last thing the party needs is to also have to defend the seat currently held by U.S. Sen. Robert Menendez.

Menendez, D-N.J., remains in legal jeopardy as U.S. District Judge William Wallis dismissed a motion last week by his lawyers to dismiss the corruption charges against him, thus allowing his trial to continue in a Newark courtroom.

A conviction likely would end his political career. But an acquittal on all or most of the charges will require Menendez and Democratic officials to decide whether he is too damaged to seek another term in 2018, when 25 Democrats and Independents who caucus with them are up for re-election compared with only nine Republicans.

"The Democrats would have to confront that issue as a party," Republican consultant Chris Russell said. "You can be sure that the nightmare scenario for them is he survives wounded."

Despite his legal troubles, Menendez is rated as a strong favorite to win re-election in 2018 by the two Washington-based publications that track Senate races, the Cook Political Report and Inside Elections.

"Senator Menendez looks forward to being exonerated and it'll be full speed ahead onto the re-election campaign next year," said his senior political adviser, Mike Soliman. "Exoneration will make it very difficult for Republicans to make a persuasive argument against the senator next year."

Still, two recent polls indicate strong disapproval of Menendez, In a Suffolk University/USA Today Network survey, 46 percent viewed him unfavorably and just 20 percent had a favorable opinion of the senator.

In a Quinnipiac University poll, Menendez's job approval rating dipped to 31 percent, his lowest rating since February 2008, while 49 percent disapproved.

Democrats say it's still too early to speculate about 2018.

"To say this is going to hurt Bob Menendez in an election that's over a year away, I don't you can make that case now," said Bill Caruso, former executive director of the state Assembly Democrats.

"Folks are keeping an eye on the trial but most people are not going to come to any conclusions," Caruso said. "There will a question about polling and conversations about how strong Bob Menendez is and what are the chances going into next fall."

That will wait until after the governor's race is run next month, and what happens in that Newark courtroom.

The Senate race looms larger now in an era when Republican efforts to repeal the Affordable Care Act and increase the number of uninsured Americans by as many as 32 million failed by just one vote.

"This is certainly a time in our history where so much is at stake in every single one of these U.S. Senate seats," said Matt Canter, a former official at the Democratic Senatorial Campaign Committee. "There is a tremendous amount of work cut out for Democrats just to hold the line."

New Jersey hasn't elected a Republican to the Senate since Clifford Case in 1972.

So even if he's acquitted, Menendez may decide not to seek re-election, especially if he is seen as a weak incumbent and Democrats in a primary and Republicans in a general election are lining up to challenge him, observers say.

"After all he's been through, it would be perfectly reasonable for Senator Menendez to step down and let somebody else run," Democratic consultant Glenn Totten said. "He may very well say, 'It's time for new blood.'"

Russell, the Republican consultant, said he can't see Menendez just walking away.

"The number of people who willingly walk away from the United States Senate, you and I can count on two hands," Russell said. "His ambition may get in the way of his sense."

But Matthew Hale, a political science professor at Seton Hall University, said he didn't think Menendez wanted to be remembered as someone who ended the Republicans' 40-year losing streak.

"Menendez knows when to step aide," Hale said. "You're talking legacy, not job, at that point."

Jonathan D. Salant may be reached at jsalant@njadvancemedia.com. Follow him on Twitter @JDSalant or on Facebook. Find NJ.com Politics on Facebook.