Rep. John Conyers Jr. (D-Mich.) questions witnesses during a House Judiciary Committee hearing in October. (Drew Angerer/Getty Images)

Rep. John Conyers Jr. (D-Mich.) isn't the first national politician to face credible allegations that he sexually and verbally harassed women since the Harvey Weinstein scandal erupted. But he could be the first to resign. The Washington Post reports that House Democratic leaders are pressuring him to quit the job he's held for more than five decades, even before a House ethics investigation into Conyers revs up.

That raises a question: In the wave of sexual harassment allegations hitting Washington right now, what makes Conyers the potential first to lose his job for them? There are a couple of nuanced answers to that. Let's explore how his situation seems to be different from the other national politicians.

1. The alleged misbehavior happened while he was a sitting member of Congress: All of Conyers's accusers say he acted inappropriately to them while he was actually on the job as a congressman. In an article published Tuesday in the Detroit Free Press, for example, a former staffer accused him of inappropriately touching her twice.

Many of President Trump's and Alabama GOP Senate candidate Roy Moore's accusers say the incidents happened years, even decades, ago. At least in Congress, there's an unwritten rule about being very cautious about punishing or kicking out a colleague for something he or she did before they were a member of Congress.

2. Conyers appears to be listening to his colleagues: Senate Republican leadership doesn't care that Moore's allegations center on stories from four decades ago. They want him to drop out of the Alabama Senate race now. “I believe the women,” Senate Majority Leader Mitch McConnell (R-Ky.) said.

But Moore is refusing to listen to them and instead blaming them for the controversy. He got reinforcements from the president himself, who basically endorsed Moore.

Conyers also denies doing anything wrong. But unlike Moore, he appears to be taking his Democratic colleagues' suggestions to resign seriously: He stepped down from his powerful job as the top Democrat on the House Judiciary Committee. He didn't show up for votes Tuesday night, and he was spotted on a plane flying back to Detroit instead.

Also unlike Moore, Conyers is firmly a member of the establishment. He is the longest-serving House member and he helped found the Congressional Black Caucus. Now that members of that organization are urging him to step down, he can't spin this as the party out to get him.

3. Defending Conyers backfired: On Sunday talk shows, House Minority Leader Nancy Pelosi (D-Calif.) called Conyers an “icon” and had cause to immediately regret it. Women's advocates and rights groups blasted Pelosi for backing an accused sexual harasser.

By Monday, Pelosi basically retracted that by saying she talked to and believes one of his accusers, ethics lawyer Melanie Sloan. By Tuesday, The Post reported she was asking Conyers to resign.

By contrast, no Senate Democrat has tried to defend Sen. Al Franken (D-Minn.), whom four women now accuse of sexual harassment. After the first allegation, they in unison called for the Senate's ethics committee to investigate him, and they haven't really felt pressured to go any further yet.

4. Politics, politics, politics: Politics is inextricably linked to any sexual harassment allegation leveled against a politician.

Trump has basically said he supports Moore because he doesn't want a Democrat to win that Senate seat.

No Senate Democrat has publicly said this, but it's a political reality that if Franken resigns or is forced out by a Senate ethics investigation, Republicans could win his Senate seat.

But if Conyers goes, Democrats will probably keep his deep-sea blue Detroit-area district. Politico reports there's also a sense among some of Conyers's colleagues that he has been in Congress long enough (53 years), sexual harassment allegations or not.

Politico also reports Democrats fear more credible allegations against Conyers could be coming, so they feel as if they need to get out ahead of the situation now by forcing him out rather than muddle through a messy and lengthy House ethics investigation.

That brings us to our last point: Both parties have been tarnished in this recent wave of sexual harassment allegations. But if there's a way for Democrats to seize the moral ground in this, they'll likely take it, especially with the possibility of unseating Trump in 2020 on the line. And for now, that apparently means they think Conyers has got to go.