Democratic presidential candidate John Delaney, a former congressman from Maryland, waves before speaking during the California Democratic Party convention in San Francisco on Sunday. (Jeff Chiu/AP)

The campaign of John Delaney, who has struggled to get attention in the crowded Democratic presidential field, escalated a fight Monday with Rep. Alexandria Ocasio-Cortez (D-N.Y.) over the wisdom of a “Medicare-for-all” health-care system.

Delaney, a former congressman from Maryland who has tried to find a moderate lane in the race for the White House, was booed during an appearance Sunday at the California Democratic Party convention when he said “Medicare-for-all may sound good, but it’s actually not good policy nor is it good politics.”

The episode prompted Ocasio-Cortez, one of the most visible liberal members of Congress and a vocal proponent of single-payer health care, to take to Twitter to suggest Delaney exit the race.

“Since there’s so many people running for President (& not enough for Senate), instead of obsessing over who’s a ‘frontrunner,’ maybe we can start w some general eliminations,” she wrote. “John Delaney, thank you but please sashay away.”

Sunday night, Delaney issued a challenge to Ocasio-Cortez via Twitter to debate health-care policy on any television show of her choosing.

And Monday morning, Delaney’s campaign took another shot at the freshman lawmaker.

“The only person Congresswoman Ocasio-Cortez helped with her tweet about Congressman Delaney was Donald Trump,” Michael Starr Hopkins, Delaney’s national press secretary, said in a statement.

“2016 should have taught us that if we allow this primary to become a popularity contest on Twitter rather than a debate of ideas in the public square, the country will lose,” Hopkins continued. “We’ve seen this playbook before and it ends with a second term for Donald Trump.”

Delaney, who has gained little traction in polling despite his early entrance into the race, has issued his own universal health-care proposal that calls for the creation of a new public plan for all Americans under the age of 65 while maintaining the traditional Medicare system for those above that age.

Under his plan, individuals would be allowed to opt out of the new system and receive a tax credit to buy their own insurance policy if they choose, and individuals and employers could negotiate supplemental coverage from private insurers.