Democratic presidential candidate Martin O'Malley criticized front-runner Hillary Clinton for opposing President Obama's international trade agreement "on the eve of the first Democratic debate."

O'Malley, a former Maryland governor, said on CNN's "State of the Union" that he has opposed the plan -- which is panned by liberal labor groups -- for eight months, citing concerns about worker protections.

"I didn't shift positions right on the eve of the first Democratic debate," O'Malley said on CNN, alluding to Clinton, who came out against the plan last week.

O'Malley has struggled to break out of single-digit polling and has been largely eclipsed by Sen. Bernie Sanders (I-Vt.), who has surged in polling as the Democratic alternative to Clinton.

Sanders also opposes Obama's trade plan, known as the Trans Pacific Partnership (TPP). Clinton helped establish the groundwork for it during her time as secretary of State.

O'Malley said he's not worried about his low polling, noting that he's focused on Tuesday night's Democratic debate -- the first of the cycle.

"This race is really just beginning for the Democratic Party," O'Malley said.