Who Will Win the Race Within the Race?

Though Mr. Cruz benefited from Mr. Rubio’s weak performance in Kentucky and Louisiana, it is not clear whether he can make the same gains in Michigan. It is a blue state with relatively few evangelical voters, and Mr. Cruz has struggled so far in such states.

Instead, Mr. Kasich could be the candidate who benefits from Mr. Rubio’s struggles. He is a relatively moderate governor from a neighboring state, and polls show he has moved into a tight race with Mr. Cruz for second place.

The race for second is a test for both Mr. Cruz and Mr. Kasich as each looks to present himself as the strongest Trump alternative. The second half of the primary season includes many Democratic-leaning states, like California, New Jersey and New York. A strong second-place showing in Michigan would ameliorate concerns about Mr. Cruz’s ability to compete in blue states; if Mr. Kasich were to fare better, it would set him up for a strong showing in his home state next week.

Is Michigan Sanders’s Best Bet?

On paper, Michigan should be a good state for Mr. Sanders. It is a white, working-class state that has been ravaged by outsourcing and ought to be receptive to Mr. Sanders’s message on economic issues. It is also a fairly liberal state, with big college towns like Ann Arbor and East Lansing. The state is whiter than the nation as a whole, and black voters — who have turned out in droves for Mrs. Clinton in the South — make up roughly the same share of the electorate there as they do nationally.

The burden for Mr. Sanders in Michigan is even higher because he needs to make up for losses in the first part of the primary season with even stronger showings going forward. The polls suggest that Mrs. Clinton is on track for a decisive victory, so Mr. Sanders needs a surprise win to show he still has a path of his own.