Almost one in five New Hampshire Democratic primary voters cast their ballots Tuesday for someone other than Barack Obama.

The president still won the primary with a handsome majority: 81.9 percent of the vote.

But the fact that more than 18 percent of New Hampshire voters who took Democratic primary ballots chose to write in the name of another candidate—anti-war Republican Ron Paul was the second-place finisher in the primary with 2,273 write-ins—or to vote for one of the little-known contenders whose names were on the ballot with Obama’s begs a question: What if a prominent progressive had mounted a primary challenge to the president?

Consumer activist Ralph Nader, scholar Cornel West and others argued for such a challenge last year. And Senator Bernie Sanders, Congressman Peter DeFazio and Congressman Dennis Kucinich were among the Capitol Hill progressives who suggested it would be good for the party and the president to face a meaningful primary test. While inside-the-party wrangling might be messy, the argument went, Democrats would ultimately be well served by an airing of the issues and a pressuring of the president to focus and intensify his outreach to the party’s base voters.

The project never came to fruition. So the New Hampshire primary votes cast for someone other than Obama were scattered and drew little attention as the media obsessed about the Republican primary fight. The same was the case after last week’s Iowa’s Democratic caucuses, where caucus-goers in liberal-leaning communities such as Iowa City and Ames selected a small but notable number of uncommitted representatives to participate in the process of choosing delegates to this summer’s Democratic National Convention.

Ultimately, Obama will secure all the DNC delegates from Iowa and New Hampshire.

And his supporters will make the case that whatever dissent that may be surfacing is relatively normal.

After all, the last sitting Democratic president to run in a New Hampshire Democratic primary, Bill Clinton in 1996, took just 84 percent of the vote.

Clinton went on to win New Hampshire with relative ease in November 1996.

But there are some other numbers that should concern Obama and his Democratic allies.

While Obama’s New Hampshire Democratic primary vote percentage in 2012 was roughly the same as Clinton’s in 1996, their actual vote totals were dramatically different.

Clinton won 76,797 votes out of a total 91,027 votes cast in the 1996 Democratic primary.

Obama won 49,480 votes out of a total of 60,996 votes cast in the 2012 Democratic primary.

The Democratic primary turnout this year was down dramatically (roughly 33 percent) from 1996, the last year when a Democratic president was seeking re-election without meaningful opposition. By contrast, 2012 Republican primary turnout was up by almost 39,000 votes, an increase of roughly 16 percent, from 1996.

In 1996, when Republicans had an intense contest (Pat Buchanan beat Bob Dole by a handful of votes), more than 30 percent of all primary voters in New Hampshire participated in the low-profile Democratic contest.

In 2012, when the Republican race was significantly less intense (Romney maintained a reasonably steady polling lead and won with ease), less than 20 percent of all primary voters in New Hampshire took Democratic ballots.

Barack Obama ought not worry about the percentage of the vote he took in this year’s New Hampshire Democratic primary. It was sufficient.

But the president and his campaign aides should be paying attention to the evidence of an enthusiasm gap when it comes to voting in the Democratic primary of will be a battleground state this fall. And they should be asking themselves whether that gap in just a New Hampshire concern, or if might be a problem in other battleground states where Obama may not have much margin for error.