Mitt Romney's victories on Tuesday in the Republican presidential primaries in Michigan and Arizona reflect his ability to do what he needed to do.
Mr. Romney had to win in Michigan, his native state, where his father was governor. He beat Rick Santorum by a narrow three percentage points despite his continued opposition to the federal bailout of the U.S. auto industry, an unpopular position in Michigan.
And he won in socially conservative Arizona by 21 points, giving him all of that state's delegates to the Republican National Convention. Exit polls suggested that voters were looking for the candidate they think most capable of beating President Obama in November.
The outcomes in Arizona and Michigan could mean that Mr. Romney has fought off the most recent challenge to his front-runner status. If Mr. Santorum has peaked prior to a decline, that would replicate the track record of previous Republican candidates Donald Trump, Herman Cain, Michele Bachmann, and Rick Perry, all of whom flagged as voters took a closer look at them.
A strong performance in next week's Super Tuesday primaries, especially in Ohio, could ice the nomination for Mr. Romney. But despite his advantages in fund-raising and organization, he has yet to close the deal with Republican voters.