President Donald Trump was not on stage for Monday night’s debate between Democratic Sen. Ed Markey and his Republican challenger attorney Kevin O’Connor, but he showed up in several of the questions and clearly remains the driving theme in both campaigns.

Markey immediately and repeatedly tried to tie O’Connor to Trump and Senate Majority Leader Mitch McConnell.

“You know you’re a Donald Trump Republican when you don’t wear a mask yourself in public, like Mr. O’Connor,” Markey said, launching into a series of issues that prove O’Connor is a “Trump Republican.”

O’Connor, an attorney, raised several issues where he disagrees with Trump and McConnell. He said, for example, that he does not support the ongoing litigation pending before the Supreme Court to eliminate the Affordable Care Act and he believes climate change is a real threat. But he also said he supports the president. Trump “represents the best opportunity for us to have safe neighborhoods, not open borders, sanctuary state, not defunding and disarming of the police the way Sen. Markey advocates,” O’Connor said.

O’Connor repeatedly returned to the theme that Markey is an extremist with views even to the left of Democratic presidential nominee Joe Biden. O’Connor noted that Markey supports both the Green New Deal — a sweeping bill to reduce carbon emissions and fight climate change — and a government-run health care system dubbed Medicare for All, both of which Biden has rejected.

Markey also went beyond Biden on the Supreme Court, saying that McConnell and Republicans had “swiped” a Supreme Court seat from President Barack Obama by refusing to confirm Merrick Garland in 2016. Now Republicans are rushing to confirm Trump nominee Amy Coney Barrett to replace Ruth Bader Ginsburg. If they succeed, Markey said, it is “very much necessary” to “begin a discussion of enlarging the Supreme Court.”

During a debate with Trump last week, Biden refused to take a position on expanding the number of justices on the court.

While the debate highlighted the clear ideological differences between the candidates, it did not appear to offer any dramatic moment that might fundamentally alter the race.

O’Connor faces a number of daunting hurdles running as a Trump-friendly Republican in a state where the president is wildly unpopular. By the middle of August, Markey had raised more than $12 million for the Senate campaign; O’Connor has raised less $500,000.

And there are far more Democratic than Republican voters in the state. About 1.4 million people cast ballots in the Democratic primate between Markey and Rep. Joe Kennedy on Sept. 1 while about 265,000 people cast ballots in O’Connor’s primary against tech entrepreneur Shiva Ayyadurai. However, more than half the state’s 4.6 million voters are “unenrolled” in either party.

Even before the debate began, the two sides were sparring over COVID. Markey announced on Twitter Sunday that he had taken a COVID test prior to the face-to-face matchup. O’Connor refused to say whether he has been tested and on Monday his campaign accused Markey of attempting to use the issue as an excuse to avoid the one debate they have agreed to.

“I understand that the Markey campaign has been trying to drum some things up,” O’Connor said on Facebook Monday. “I want everyone to know I’ve complied completely with the rules and we’re ready to go and the debate is on.”

A few hours before the debate began, GBH announced that the two candidates would be broadcast from separate studios “in an effort to ensure the greatest individual comfort and safety of everyone involved with the debate,” a spokeswoman said.

O’Connor complained about these changes in the opening moments of the debate, and moderator Jim Braude apologized. “We did change the rules late, because our view is the world changed Friday” with Trump’s COVID diagnosis, “and we tried to change with it,” Braude said.

As to who is to blame for the more than 200,000 Americans have died from the coronavirus, Markey said Trump was “criminally negligent” in failing to “provide the moral and personal leadership the American people needed.” O’Connor said Markey has failed to point out “the fault of the communist Chinese Party in causing all of this,” which is part of a “long record of weakness in terms of dealing with China.”

While the debate highlighted the clear ideological differences between the candidates, it did not appear to offer any dramatic moment that might fundamentally alter the race.

O’Connor faces a number of daunting hurdles running as a Trump-friendly Republican in a state where the president is wildly unpopular. By the middle of August, Markey had raised more than $12 million for the Senate campaign; O’Connor has raised less $500,000. And there are far more Democratic than Republican voters in the state. About 1.4 million people cast ballots in the Democratic primate between Markey and Rep. Joe Kennedy on Sept. 1; about 265,000 people cast ballots in O’Connor’s primary against tech entrepreneur Shiva Ayyadurai.