The nomination appears beyond the grasp of Sen. Bernie Sanders, and he is under increasing pressure from Democratic elites to drop out. The delegate numbers tell a bleak tale. Including yesterday's primaries, Clinton leads him by 826 delegates (2,097 Clinton, 1,271 Sanders). Sanders could counter that the electoral terrain on Tuesday favored Clinton and the terrain going forward is more favorable to him. His campaign has the money to continue and the reasonable argument that even voters in late-voting states deserve a choice. Still, Sanders can't catch Clinton unless the dynamics of the campaign are radically altered.

That doesn't mean, however, that it's time for him to go.

Democratic primaries and caucuses award delegates proportionately. Even if Sanders were to win all of the states that have not awarded delegate thus far, he would have to win approximately 80 percent of the remaining vote to surpass Clinton and capture the nomination based on pledged delegates. His widest margins of victory in the primary states that have already voted were in Vermont (86 percent) and neighboring New Hampshire (61 percent). In other states holding primaries, Sanders never exceeded a 60 percent margin. In caucus states, Sanders has done much better, winning close to 80 percent of the delegates in state like Utah and Alaska. The bad news for Sanders, as if he needed more, is that most of the states going forward are holding primaries rather than caucuses (11 primaries, 3 causes). Two of the caucuses are in territories – Guam and the Virgin Islands – that award only 7 pledged delegates each. Moreover, most of the primaries going forward (8 out of 11) are closed or semi-closed, meaning they do not allow independents to participate. Sanders has generally done better in open primaries where he tends to garner substantial independent support.

It would seem to be an open and shut case: Sanders can't win the nomination and for the sake of the party he should drop out. But, in politics, it is never that simple.

Sanders might justify staying in the race because he wants to influence the platform. This reasoning is dubious, because Sanders has already won enough support to demand significant concessions on the platform. He has also managed to force Clinton to the left on economic issues, particularly tougher Wall Street regulation and on economic inequality. It is not clear that winning more delegates will push her further to the left. The more compelling reason that Bernie should stay in the race is that he could still win.

If Clinton is indicted, the superdelegates over whom she holds a commanding lead could massively desert her. The only thing that binds them is their promise, a promise few would hesitate to break if they were convinced that Clinton would lose in the general election. Without the superdelegates, Clinton will not get to 2,383, the number of delegates she needs to win on the first ballot. Her current lead of 826 delegates would shrink to 308 pledged delegates. If all of the superdelegates shifted from Clinton to Sanders, admittedly an unrealistic hypothetical, Sanders would actually lead Clinton by 210 delegates. If the convention requires multiple ballots, with each successive ballot more delegates will become unpledged.