Democratic presidential candidate Martin O'Malley failed to qualify for Ohio's primary ballot after falling short of the signatures needed to appear before the state's voters, a spokesman for the state's elections chief said Thursday.

O'Malley needed 1,000 valid signatures to appear on the March 15 primary ballot. The former Maryland governor's campaign submitted 1,175 signatures, but only 772 were deemed valid, said Josh Eck, a spokesman for Ohio Secretary of State Jon Husted.

O'Malley's campaign expressed disappointment, though it noted the candidate is on the ballot in 18 other states.

"While this news is disappointing, we are exploring all of our options, and Gov. O'Malley will campaign vigorously in Ohio," spokeswoman Haley Morris said in an emailed statement.

O'Malley is running an underdog bid for his party's nomination against Hillary Clinton and Bernie Sanders. Both Clinton and Sanders were certified for Ohio's presidential primary ballot, along with a little-known candidate, San Diego businessman Roque "Rocky" De La Fuente.

Clinton already has the support of some key Democratic insiders in Ohio, where she won the 2008 primary over Barack Obama.

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