Democrats have mounted a fairly successful resistance to President Trump's agenda in the U.S. Senate. They managed to prevent Obamacare repeal by one vote. And with the noteworthy exceptions of judicial nominations and a limited number of regulatory repeals, they have had the numbers they needed to prevent most permanent legislation from passing.

But there's a bit of unspoken anxiety this month. Because for reasons that have nothing to do with Trump or Senate Republicans, there's a non-trivial chance that one of the 48 seats in their caucus could be taken away and given to a Republican by year's end.

In spring 2015, Sen. Bob Menendez, D-N.J., was indicted by a grand jury on some very serious bribery and corruption charges. This wasn't the result of anyone's partisan vendetta. The grand jury had been convened, and the evidence presented to it, by prosecutors appointed by President Barack Obama, months before Donald Trump announced his candidacy for president.

Menendez's trial began this month. His attorneys tried to slow the process down, but to no avail. And that ruling could have serious consequences if it hastens a guilty verdict.

The trial is supposed to run somewhere into November. But let's just say the jury finds Menendez guilty before Thanksgiving. In theory, whoever is appointed to replace Menendez will be able to serve until November 2018.

Until Jan. 16, 2018, Republican Chris Christie will be governor. After that date, it is highly likely that a Democrat will replace him. So ... how long do you suppose Menendez could hang on to his seat if he were convicted? And how long would Democrats help him cling to it in order to avoid losing that last deciding vote that stopped Obamacare repeal?

There are no rules that would force Menendez to step aside upon conviction. Unless and until two-thirds of your peers vote to expel you from the Senate – which in this case would require votes from at least 15 Democratic senators – you can hold on to your seat for just about as long as you and your party can stand the heat. The non-partisan Congressional Research Service puts it this way:

Members of Congress do not automatically forfeit their offices upon conviction of a crime that constitutes a felony. No express constitutional disability or "disqualification" from Congress exists for the conviction of a crime, other than under the Fourteenth Amendment for certain treasonous conduct by someone who has taken an oath of office to support the Constitution. Unlike Members of the House, Senators are not instructed by internal Senate Rules to refrain from voting in committee or on the Senate floor once they have been convicted of a crime which carries a particular punishment. Internal party rules in the Senate may affect a Senator's position in committees.

So, with that in mind, think of the math. As long as Menendez's rear is still warming that seat – even if he is too busy mopping prison floors to attend Senate floor votes – Republicans still would need 50 senators' votes to pass anything. (They just wouldn't need Mike Pence to break ties anymore.) That means that in the event of a conviction, Democrats could avoid any of the consequences of a diminished minority – even short-term consequences – if they can just keep him from resigning or being removed until mid-January.

But then how far would Senate Democrats be willing to go in order to spare Menendez until Jan. 16, 2018? If a conviction comes down sooner than expected, they might have to spend two months or more protecting a convicted bribe-taker for partisan gain. Surely, there would be political consequences.

Yes, they could argue that Menendez's appeals haven't been exhausted. And if it comes to a vote, they could also have the nine or ten most vulnerable Senate Democrats up for reelection next year (the Claire McCaskills and Joe Donnellys of the world) vote to expel him, while everyone else takes one for the team.

But voters might just not be that stupid. So, the best thing for the Democrats to do at this point is to pray for an acquittal, or at least hope that there's no conviction until mid-to-late December.