Donald J. Trump doesn’t always seem like a candidate focused on expanding his base of support. He may have done so anyway.

The share of Americans who say they have a favorable view of him has increased significantly since the 2016 election.

And over the last few months, some of the highest-quality public opinion polls, though not all, showed the president’s job approval rating — a different measure from personal favorability — had inched up to essentially match the highest level of his term.

The increase in his support since 2016, and the possibility that it continues to move higher, does not necessarily make him a favorite to win re-election. His job approval ratings remain well beneath 50 percent, and have never eclipsed it. But it has some important implications in how to view his re-election prospects.