Some viewers questioned whether Democratic candidate Martin O'Malley was actually vying for the vice presidential position in the 2016 election. GETTY IMAGES

On the campaign trial, Martin O'Malley has not been hesitant to launch attacks against Hillary Clinton, but while on stage at the first Democratic debate Tuesday, the former Maryland governor appeared amicable toward the party's front-runner. His demeanor raised the question: Is O'Malley vying to join the 2016 Clinton ticket?

When Clinton's email controversy was addressed, O'Malley did not seize on the opportunity to criticize her on the use of a private email server during her tenure as secretary of state. Instead, he said the debate should be focused on issues that affect American voters more.

"I believe that now that we're finally having debates, Anderson, that we don't have to be defined by the email scandal, and how long -- what the FBI's asking about," O'Malley said. "Instead, we can talk about affordable college, making college debt free, and all the issues. Which is why -- and I see the chair of the DNC here, look how glad we are actually talking about the issues that matter the most to people around the kitchen table."

Even when O'Malley slighted Clinton, he took a cordial approach. "I respect what Senator Clinton and her husband have done ... but I think we need new leadership."

Blue Nation Review has speculated about a Clinton-O'Malley ticket. "Yes, ladies and gentleman, O’Malley is running for vice president. He is also, it seems, running to be Clinton’s conscience," the left-wing blog wrote.

Pundits said to stand out Tuesday, O'Malley would need to take strong positions against Clinton. His presidential run has largely been eclipsed by the campaigns of Clinton and Vermont Sen. Bernie Sanders, who both are dominating polls. In the latest CBS poll, O'Malley earned less than 1 percent of support from Democratic primary voters.

"There is nobody for whom the stakes are higher than Martin O'Malley," Mo Elleithee, former communications director at the Democratic National Committee, told NBC News before the debate. "This is a make or break moment."

Martin O'Malley Presidential Candidate Profile | InsideGov

Some criticized O'Malley's overall performance, but praised his closing remarks. The former Maryland governor highlighted the difference between the Democratic and Republican debates, noting there were no racist or sexist remarks on stage Tuesday. "What you heard on the stage was an honest search for the positions that will move us forward," O'Malley said.

Viewers took to Twitter to applaud his statements. "O'Malley's best moment of the night. Showing what America is really about. Great job," wrote one Twitter user.

Even in his home state, O'Malley has failed to garner significant support. The former governor received just 4 percent of the vote from Democratic primary voters in Maryland, according to the latest Washington Post poll.

In addition to Clinton and Sanders, the former Maryland governor was joined on stage Tuesday by former U.S. Sen. Jim Webb of Virginia and former Rhode Island Gov. and U.S. Sen. Lincoln Chaffe. CNN invited Vice President Joe Biden, who has not declared his candidacy, to the debate, but he did not participate.

The debate was broadcast by CNN at 8:30 p.m. EDT Tuesday from the Wynn Casino in Las Vegas. CNN anchor Anderson Cooper was tapped to moderate the debate, and chief political correspondent Dana Bush and CNN en Espanol anchor Juan Carlos Lopez also asked questions.