After presidential primaries or caucuses in 28 states, voters are sending a potentially troubling message to the Republican Party: We aren’t necessarily as excited about the campaign as you think.

By some important measures, voting analysts say, turnout is down in the Republican nominating contests compared with 2008, defying the widespread assumption that Republicans would line up in huge numbers for a chance to evict President Obama from the White House.

There is some encouraging news for Republicans. Some gauges of voter intensity continue to show Republicans far more enthusiastic about this election than are Democrats; a New York Times/CBS News poll this month found that 40 percent of Republican primary voters say they are more enthusiastic than usual about voting in the presidential election this year, compared with 29 percent of Democrats. And the overall number of people voting in the Republican primaries is up slightly compared with four years ago.

But despite the spirited battle between Mitt Romney and a succession of challengers, turnout as a percentage of the eligible voting population is down, and the states where turnout is up are often those that allow Democrats and independents to vote in Republican contests.