If Franken stays, that strategy loses a great deal of potency. People like Manchin may say they're only demanding different punishments for different levels of alleged misconduct. But it will come off as partisan hypocrisy and circle-the-wagons tactics.
2. All indications point to the fact that this harassment scandal hanging over Capitol Hill is just beginning. Remember, we just found out last month that there are still more than 260 documented cases since 1997 of sexual harassment and misconduct by members of Congress and their staffers. These are just the cases that included $17 million in cash settlements paid for by the taxpayers.
Right now, the names of the accused in those settlements remain sealed. But the chances of those settlements remaining secret are fraying by the day. Members of both parties have recently introduced bills to unseal those deals, and they could be leaked at any time.
Several reports say the tension is rising on Capitol Hill as some expect 30 to 50 members of Congress to be forced out just in the coming months when more misconduct cases are revealed.
If any Democrat thinks he or she can just ride out this wave and the worst is over, they're wrong. Someone like Senator Franken, who already promised to resign, seems like the least likely candidate to weather the storm.
3. Minnesota Governor Mike Dayton has already appointed his current lieutenant governor Tina Smith to replace Franken. Does Franken really want to hang on and literally deny a woman her opportunity to take a promised leadership role?
As they say in politics, that's bad optics on top of bad optics.
All of the above reasons are a perfect recipe for political suicide. Right now, the Democrats have big leads in all the major generic ballot polls for the 2018 midterm elections. Issues like President Trump's unpopularity and dislike for the tax reform bill are putting the wind at the Democrats' backs.
But the sexual harassment backlash story is shaping up to be an even bigger story in 2018 and could easily distract the voters from the Democrats' current advantages.
With that in mind, the question for the Democrats isn't whether they should encourage Franken to stick around but why they aren't pushing him to resign sooner.
Commentary by Jake Novak, CNBC.com senior columnist. Follow him on Twitter@jakejakeny.
For more insight from CNBC contributors, follow @CNBCopinion on Twitter.