Yahoo! Politics Senior Editor Dylan Stableford writes:

First it was Hillary Clinton's "damn emails" that Bernie Sanders said Americans were sick and tired of hearing about.  Now it's Bill Clinton's sex life.

"We have more things to worry about than Bill Clinton's sexual life," Sanders said on ABC's "This Week" Sunday.

The Vermont senator and Democratic presidential hopeful repeated the line on CNN's "State of the Union" Sunday.

And, most recently, at a town meeting in Iowa:

[W]hat Bill Clinton did was totally, totally, totally disgraceful and unacceptable.  But I am running against Hillary Clinton, not Bill Clinton."

Sanders added that this campaign should be about the issues, not Bill Clinton's sex life.

Agreed.  But what about Hillary's conduct, on the other hand, in ridiculing, vilifying, and attacking the credibility of each and every one of Bill's accusers?  Is that not fair game for the candidate who holds herself out as a women's advocate and feminist role model?  If Hillary wants to do the I-am-woman-hear-me-roar shtick, how is it unfair, say, to ask her whether she believes Juanita Broaddrick?

Also fair game are the "damn emails" about which Sanders says the American people are sick and tired of hearing.  Fair enough, if one equates liberal Democrats with "the American people," which, of course, is what liberal Democrats do.  As for the rest of us, who expand the definition of American people to include the 80% of the electorate who are not liberal Democrats – well, who thinks the reason the State Department released 2,900 Hillary emails at 1:00 a.m. is because Americans would not be interested?

On the other hand, in fairness to Bernie Sanders, the American people are not interested in all of Hillary's emails – just the classified ones.  As is the FBI.

Call this writer a skeptic, but it has been his experience that when a politician says that he is "not interested" in hearing about something, it means that others, who he would prefer do not hear about it, are.

But Bernie Sanders says that he is not interested in how confidential State Department documents got onto an unsecured server chez Clinton, or how Hillary Clinton betrayed every credible victim of sexual harassment, assault, or even rape by acting as her husband's enabler.  Okay.  Fine.

But if Sanders isn't interested, one must ask: why not?

More important, why is trying to dissuade the American people, whose votes he says he is seeking, from learning facts that would, if true, hurt his opponent, Hillary Clinton, and help him?

Why is Bernie Sanders constantly running interference for Hillary Clinton on two of her most serious vulnerabilities?

Does Bernie Sanders want to be president of the United States.  Or not?

Were Sanders a Clinton campaign staffer or even just a grassroots Clinton supporter, defending her from attacks on two issues on which she is eminently vulnerable – her mishandling of classified information and her attacks on multiple women who accused her husband of various levels of sexual harassment, including rape – would make sense.

But Sanders is running against Clinton.  Never mind not defending Clinton against attacks by others.  Why is he not attacking her himself?

Again: Does Bernie Sanders want to be president?  And if he doesn't really, really want to be president, why is he campaigning?  To bask in the adoration of the crowds?

Why does he express dissatisfaction with the number and timing of the Democratic debates?  Because they provide insufficient opportunities to praise Hillary Clinton?

Is there some secret pact with the Clinton campaign whereby Sanders agrees to pose as some kind of "symbolic opposition" to avoid appearance of a Hillary coronation?  With the promise of a cushy position in a future Clinton administration if she wins – and at the Clinton Foundation if she loses?

Or maybe, like so many of our friends on the left, Bernie Sanders simply dislikes Republicans so much that he would rather lose the Democratic primary than echo and thus validate Republicans' criticisms of Hillary.

And if, as seems increasingly likely, the FBI recommends that the Justice Department indict Clinton, will Sanders still hold his tongue, even if it means possibly watching their candidate and possibly the entire ticket, who will have been complicit before the whole country in acting as her enablers, go up in flames?

Bernie Sanders says he wants to be president.  He is campaigning.  He is appearing on talk shows.  He is taking donations.  But he is not fighting – not really.  He is not exploiting his opponent's weaknesses, not using every legitimate weapon at his disposal, even those provided by the Republicans.

Why not?

Call him the inscrutable Mr. Sanders.

Gene Schwimmer is a New York licensed real estate broker and the author of The Christian State.  Follow Gene Schwimmer on Twitter.