I think should John McCain should drop out of the race now:
1) Delegates: he hasn’t won any pledged delegates to the Democratic Convention, and his only superdelegate has been asked to leave, so he has to no chance of getting the Democratic nomination.
2) Spoiler: If he stays in, he may end up the nominee of another party, spoiling the chance for the Democratic nominee to be annointed President in August.
3) Mudslinging: He has had no qualms about attacking the Democratic frontrunners, pointing out that they are both anti-American drug addicts. This seems set to continute throughout the year.
4) Appeal to Independents: McCain may draw votes from the critical swing voters we need to win over. He has the same position on climate change and immigration as Obama and Clinton. He could cut into Clinton’s support among people who like talk about experience, or Obama’s support among people who like talk about bipartisanship, as he also talks about those things.
So, in conclusion, John McCain should drop out of the race for the presidency for the good of the Democratic Party.