Aurora, Colorado (CNN) Republican Rep. Mike Coffman faced angry constituents at a town hall Wednesday night, in an early sign of the political price he and his colleagues might pay for supporting President Donald Trump's policies, including the repeal of Obamacare.

A moderate hailing from a swing district, Coffman fielded more than 40 questions from Coloradans for almost two hours. Health care overwhelmingly dominated the at times raucous evening, as the congressman's constituents demanded to know why he backed a bill to gut Obamacare before it was yanked from the House floor.

More than once, Coffman was offered an ultimatum: You can side with us or side with the President.

One woman who described herself as a health care worker with pre-existing conditions said the health care bill that Trump endorsed would eliminate protections for people with medical histories.

"Are you going to side with Trump or are you going to ... stand with your constituents?" the woman wanted to know.

Coffman vowed to protect coverage for those with pre-existing conditiseons, and also insisted that he disagreed with Trump's suggestion of letting Obamacare "implode."

"I don't think that's right. Somehow he thinks that the Democrats are going to come around if it implodes," he said. "I think we need to fix it. And we need to fix it now."

For most of the evening, Coffman appeared to take the frequent "booing" in good humor.

But as the town hall approached the two-hour mark, the criticisms -- and in particular, the repeated suggestion that he wasn't holding Trump accountable on everything from his tax returns to potential business conflicts -- clearly exasperated the congressman.

The tensions came to a head with the final question of the evening, from a woman who said her great-grandparents had died in Auschwitz. She expressed dismay at what she said was a "president who has anti-Semitic people" in high-ranking positions, and slammed White House press secretary Sean Spicer for saying Syrian leader Bashar al-Assad 's actions were worse than Adolf Hitler's.

"Spicer made a terrible mistake yesterday," Coffman began. "If you're not familiar with what he did..."

But the audience let it be known that it wanted no excuses about Spicer. Throwing up his hands, Coffman finally said about Spicer: "He needs to go."

Coffman could have a tough reelection fight next year against newly announced Democratic candidate Jason Crow. Party strategists hope that Crow's background as an Army ranger who served in Iraq and Afghanistan, as well as his newcomer status to politics, will make him a strong challenger to Coffman, who was first elected to the House in 2008.

The Democratic Congressional Campaign Committee says it views the House race in Colorado's 6th Congressional District here -- an area that includes Aurora and its surrounding suburbs -- among the top 10 most competitive in 2018.

Democrats are feeling especially optimistic following a special house election in Kansas Tuesday night. GOP candidate Ron Estes won the contest by a far smaller margin than was expected in a district that Trump had won by double digits -- a warning sign of an energized Democratic base ahead of 2018.

Wednesday marked Coffman's first in-person town hall this year.

He confronted frustrated constituents during a local meet-and-greet in January, as emboldened Republican lawmakers in Washington were gearing up to repeal Obamacare. Coffman left that event early even as a crowd was waiting to get face time with the congressman -- a move that drew wide criticism.

Susan Gilbert, a high school teacher from Aurora, attended that event in January. She came to Wednesday night's town hall for another opportunity to get to know her congressman better.

A Democrat who voted for Hillary Clinton, Gilbert said she was surprised to see Coffman caught off guard by the sheer number of constituents who showed up to voice their concerns in January.

"If he was listening to the public and looking at all the letters and phone calls and postcards, he should have been more perceptive," Gilbert said.

Gilbert said immigration is among her top issues -- in large part because many of her own students are undocumented. "Many of my students are living in fear right now, some have already left the country because they are fearful of being deported," she said.

Plenty of Coffman's Republican colleagues have also faced hostile crowds back home in recent months over issues like health care reform and immigration.

Some voters have also taken on lawmakers for what they say is the GOP's inability to hold Donald Trump accountable, as an endless stream of controversies have dogged the first months of the Trump presidency. This is certain to be a major attack line that Democrats deploy in the 2018 midterms, particularly if the president remains deeply unpopular.

During the 2016 election, Coffman sharply distanced himself from then-President-elect Trump, even vowing in a campaign ad to "stand up to" his party's nominee.

But on Wednesday, some of his constituents weren't sold that Coffman was standing up to the president.

One man who identified himself as a registered Republican stood up at Wednesday's town hall to say he was "shocked" to learn of Coffman's support for wholesale repeal of Obamacare.

"That's not the way we do things here in Colorado. The ACA is the law of the land," the man said. "What will you do to revise, strengthen and bolster Obamacare?"

Phil Laxar of Centennial said Coffman's public support for the Republican proposal to repeal Obamacare was the single issue that disturbed him most.

"Our district voted strongly against Donald Trump and while Rep. Coffman was reelected, it seems like he is supporting Trump's policies instead of representing his constituents," Laxar, who voted for Clinton, told CNN.

"In particular, the recent un-American health care act, which he didn't have an opportunity to vote for but he did support publicly, which would be a disaster for the citizens of his district," he added.