Martin O'Malley's campaign fell short of enough valid signatures to secure his spot on the Ohio Democratic primary ballot, handing the former Maryland mayor yet another setback in his bid for the White House.

A spokeswoman for Ohio Secretary of State Jon Husted told The Wall Street Journal that Mr. O'Malley had submitted 1,175 signatures - well beyond the 1,000 that are needed - but only 772 were found to be valid. The deadline for submitting signatures was Dec. 16, so the O'Malley campaign cannot submit more signatures now.

O'Malley's campaign expressed its disappointment but said it was on ballots in other states and plans to continue campaigning in Ohio anyway, according to the Associated Press.

"Our campaign filed nearly 1,200 signatures for the Ohio ballot. While this news is disappointing, we are exploring all of our options, and Governor O'Malley will campaign vigorously in Ohio," campaign spokeswoman Haley Morris said in a statement published by Politico. "To date, he is already on the ballot in 18 other states."

In an average of the last five national polls, O'Malley gains the support of only 4.7 percent of those who responded, according to RealClear Politics. O'Malley has a slight bump in Iowa at 5.7 percent, but only 1.8 in New Hampshire.

The Democratic challenger is having difficulties connecting with voters in the Midwest this month. Earlier this week, he held campaign events in Iowa where turnout was low, in part because of a winter storm that struck the state. In one instance, only one Iowan showed up who remained uncommitted even after the one-on-one session.

"The very last event of the night, we actually had a whopping total of one person show up, but by God, he was glad to see me," O'Malley told MSNBC's "Morning Joe" in an interview on Tuesday, Politico reported. "So we spent the time with him."