Clinton is narrowing down her choices for running mate:

Those on the shortlist include Massachusetts Sen. Elizabeth Warren, a favorite of progressives who has emerged as a blistering critic of presumptive Republican nominee Donald Trump; Virginia Sen. Tim Kaine, a well-liked lawmaker from an important general election battleground state; and Housing and Urban Development Secretary Julian Castro of Texas, a rising star in the Democratic Party.

Kaine would seem to be the best choice of these three. In addition to having worked much more on foreign policy and war powers than Warren, Kaine was a governor from a purple state. Kaine has the relevant experience and preparation to be president that the other two simply don’t have, but choosing him would not be the attention-grabbing or “exciting” one that selecting one of the others would be. Having Kaine on the ticket would show seriousness about governing, and having someone prepared to take over in an emergency would be the responsible thing to do. Because Kaine has been leading the effort to get a vote on authorizing the war on ISIS and has been an advocate of restoring Congress’ role in matters of war, it is possible that Kaine could help check some of Clinton’s hawkish tendencies. I wouldn’t expect too much on this score, but it is something to bear in mind.

Taking Warren out of the Senate would be a mistake for Democrats, since that is where she is likely to have the greatest impact on the party’s agenda. Picking Warren would be seen as a concession to Sanders supporters, but the effect of it would be to make her a defender of whatever Clinton chose to do. Progressives would probably rather have her in the Senate acting as a critic of Clinton’s policies than as the person assigned the task of selling those policies to the left. Regardless, Warren doesn’t have much in the way of foreign policy or executive experience, and there is no obvious electoral advantage in naming a senator from a deep blue state. If Warren is not prepared to be president, Castro is even less prepared than she is, and choosing him would be a fairly odd choice in a year when the Democratic ticket isn’t going to have much trouble winning over Hispanic voters.