(CNN) Presidential candidate Beto O'Rourke on Friday refused to commit his unconditional support to Democrats down the ticket in 2020 should he secure his party's nomination, in a contentious exchange with a New Hampshire voter.

"I can't take a pledge to support every single Democrat in the country," the Texas Democrat told Deb Nelson, the chair of the Hanover/Lyme Town Democrats, during a house party in Lebanon, New Hampshire. "I need to know about them first, right? Would you want me to make a blanket commitment about people I know nothing about, who I've never met?"

Nelson challenged O'Rourke on his refusal to endorse Texas Democrat Gina Ortiz Jones, who ran against incumbent Republican Congressman Will Hurd, a Texas Republican, in the 2018 midterm elections. Hurd went on to narrowly survive the blue wave that swept through the House of Representatives by a margin of fewer than 1,000 votes

"Will Hurd, Gina Ortiz Jones' opponent, the incumbent member of Congress and a good friend of mine, was someone who, in my day job as a member of Congress representing El Paso, I was able to work with," O'Rourke told voters.

He referenced a now-famous 2017 road trip to the two took when flight delays prompted them to take a bipartisan drive from Texas to Washington, DC, in time for votes.

Nelson remained unconvinced by O'Rourke's defense.

"I get friendships, I do, but I think in this day and age where somebody befriends a Republican and legislation that we think is important doesn't get passed," she told reporters. "And I think that's a concern. I know Gina Ortiz Jones was very close to winning in her district, and I know he made a decision not to endorse her, and he could be a friend and still endorse a Democrat who's an Iraq War veteran and a strong candidate. And I'm concerned about that."

Chris Evans, O'Rourke's communications director, defended the Texan's 2018 campaign strategy and said he appeared with Ortiz Jones multiple times while campaigning in the district. Evans said O'Rourke told crowds that she would "make a truly great member of Congress."

"Additionally, the Beto For Texas campaign's voter ID information and voter contact data was shared with and available to Democrats up and down the ticket including Ms. Ortiz Jones," Evans said. "That included the voter IDs collected and created as Beto's campaign knocked 4.1 million doors, made 20.8 million phone calls, and sent 37 million text messages to Texas voters. This was in addition to the more than 750 volunteer offices we opened that benefited candidates up and down the ballot."

O'Rourke tied his bipartisan record to legislative successes.

"Well, I was working with (Hurd) at the time and was able to get stuff done. Well, we expanded mental health care access for veterans in this country. I couldn't declare as a Democrat, I had to find Republicans with whom we can get it accomplished. So that's just my governing philosophy."

After the exchange, Nelson told reporters, "I think you can be friends with Republicans, I think you can be -- you can drive across the country with Republicans, but I think when it comes to actually effecting legislative change, I don't see it in this Republican Party."

"Ask the people of Texas, what Democrat has done more to change Democrats' prospects in the state of Texas than I have?" O'Rourke asked, pointing to a series of down-ballot electoral successes in the state in 2018. "This state, which was 50th (in voter turnout), that was so red, that didn't even count, our 38 electoral votes are now in play for the next nominee from this party. We help folks, all up and down the ticket."