Joe Biden knows something about the vice presidential selection and vetting process. He went through it himself 12 years ago when Barack Obama tapped the 36-year Delaware senator as his understudy.

Now, after the pair served together in the White House for eight years, Biden is the one doing the choosing for vice president. He hasn’t yet clinched the nomination against Vermont Sen. Bernie Sanders, who is staying in the race despite a poor showing in this week’s primary elections. But facing the likelihood of strong Biden finishes in next week’s round of voting in megastates Arizona, Florida, Illinois, and Ohio, Biden can turn his attention to finding a running mate.