On the eve of six more Democrat presidential primaries, with Michigan being the biggest prize, the field of candidates has narrowed down to just three — Joe Biden, Bernie Sanders, and Tulsi Gabbard. However, as far as the Democratic National Committee is concerned, there are only two remaining. The DNC has once again changed the rules for qualification for the next debate, ensuring that Gabbard won’t be on the stage. So much for the DNC’s supposed commitment to diversity, as the party’s presidential contest has boiled down to a choice between two old white men. No wonder the DNC is seriously worried about voter enthusiasm.

Speaking of voter enthusiasm, Biden’s big Super Tuesday has most watchers concluding that he will be the eventual Democrat nominee, leading naturally to political pundits pontificating about a running mate. Biden has certainly scored the most endorsements, as all of the most competitive candidates that dropped out eagerly lined up to endorse him. That excludes Elizabeth Warren, who we assumed would throw her support behind her ideological comrade Sanders, but she has somewhat surprisingly refrained. Maybe her accusation of Sanders calling her a liar on national TV stung more deeply than many assumed.

Meanwhile, some pundits have made hay over a slip of the tongue by Amy Klobuchar over the weekend. While offering a hardy endorsement of Biden, she appeared to say she was joining “the ticket.” It may very well have been little other than her misspeaking, but there is near-universal consensus that Biden will choose a woman as his running mate, and Klobuchar could theoretically help him in the Rust Belt and most certainly in Minnesota.

Kamala Harris has thrown her hat in the ring for a Biden ticket with her endorsement over the weekend. Obviously, she waited to voice her allegiance until the most opportune moment — when it appears that Biden is on the cusp of securing the nomination. She checks both the female and minority boxes and therefore may have a leg up on Klobuchar, but it’s not clear that Harris delivers any constituency that Biden doesn’t already have.

Yet, irrespective of who Biden chooses as a running mate, his biggest hurdle is likely himself. As we have previously noted, and as many Democrats have quietly observed, Biden is looking old. Biden has always been “gaffe prone,” but it’s clear to everyone watching that his best days are behind him, that his political form has slipped.

This may be why Hillary Clinton has thus far pointedly refused to endorse him while releasing a documentary series about herself. For one thing, she may view his campaign as a sinking ship she’d rather not be on when he gets overwhelmed in a Trump victory wave. Secondly, she may be holding out faint hope that Biden, at 77, doesn’t make it to the convention and she will be there standing in the wings to “save” the Democrats from Sanders. This is obviously a long shot, but it’s also likely Clinton’s last opportunity for a shot at the presidency.

In any case, tomorrow’s primaries should make it clearer whether Sanders is able to mount any kind of a comeback or if Biden has the nomination wrapped up.