With Donald J. Trump behind in the polls, one apparent sign of hope for Republicans is the dwindling Democratic advantage in voter registration, particularly in battleground states like Florida and Pennsylvania.

But a closer look, using data from state officials and from L2, a nonpartisan voter file vendor, and Catalist, a Democratic data firm, shows far more favorable trends for the Democratic Party.

Democrats are actually registering more new voters than Republicans. In addition, more new voters are registering as independents. These voters are far younger and more diverse than the electorate as a whole, and they appear to lean Democratic. And although the total number of registered Democrats is falling, many of the voters switching parties probably have not voted Democratic in a presidential election in a long time — their party registration is finally catching up with how they actually vote.

These trends in voter registration aren’t being driven just by Mr. Trump. The changing tallies are a lagging indicator of what we already know: Many voters who used to consider themselves Democrats now vote Republican.