WASHINGTON — U.S. Sen. Cory Gardner was on the hot seat even before a new report estimated 22 million Americans would lose their health insurance by 2026 under a Republican bill the U.S. Senate could vote on this week.

Now the stakes are even higher for the Colorado Republican, who has not said whether he would back a GOP health care proposal he helped shape — though Gardner spoke more positively than not about the measure in a brief interview Monday on Capitol Hill.

“Over the weekend I had conversations with CEOs (including at least one official at) Blue Cross Blue Shield, who said their support for the bill is robust,” Gardner said of the health insurance giant. “They believe that it would markedly help stabilize the market, so I’ve got to go through each and every one of those arguments and see whether or not this achieves that.”

As for the report by the nonpartisan Congressional Budget Office, which on Monday found the loss of insurance for 22 million Americans would come with a $321 billion reduction to the federal deficit over roughly the next decade, Gardner said he hadn’t finished reading it but that he wanted a second opinion.

“We need to see some analysis outside of CBO because I think there is some information that we’ve got to get from the (insurance) marketplace as well,” Gardner said.

The degree to which Gardner is a true swing vote on the legislation, however, is a matter of debate.

The first-term senator was among 13 Senate Republicans tapped to help craft the bill — though Gardner contends he didn’t see the full text until last Thursday. His position as chairman of the National Republican Senatorial Committee also puts him in the upper tier of GOP leadership and close to Senate Majority Leader Mitch McConnell, who took the lead in writing the legislation.

Voting against the bill would put Gardner crossways with both GOP leadership and a Republican base that long has clamored for a repeal of the Affordable Care Act, also known as Obamacare.

But pressure on Gardner and other Republicans on the right has come in various forms.

Vice President Mike Pence — who has said Congress must repeal and replace the Affordable Care Act this summer — headlined a Friday fundraiser for Gardner in Colorado.

A day later, however, Gardner appeared at a retreat in Colorado Springs where conservatives criticized the Senate bill for not doing enough to unwind the Affordable Care Act. The retreat was hosted by activists tied to Charles and David Koch, two major power brokers in GOP circles.

Adding to the intrigue is the simple math of the Senate.

Republicans hold 52 seats in the 100-member chamber, and they only can afford the defections of two lawmakers if they want to pass their health care bill along a party-line vote — likely the only scenario, as Senate Democrats so far have stayed united in opposition.

Several Senate Republicans, meanwhile, have said they were unlikely to support the bill as written, which is more than enough to sink it. From a purely political standpoint, there’s the question of what Gardner would gain or lose for backing legislation currently destined for defeat.

McConnell has said repeatedly that he wants to hold a vote before lawmakers adjourn for a July 4 break, a decision that has its own political calculus. If the vote doesn’t happen by then — with the Senate out of session, and absent its usual megaphone — critics of the bill would have time to mount more opposition.

Gardner, however, has broken with leadership in saying that he’d like the Senate to take more time to review the health care legislation. He also said for the first time publicly last week that Republicans should hold hearings on the bill, a request that comes at the tail-end of several weeks of behind-the-scenes negotiations without a single Senate committee hearing.

An additional problem for Republican vote counters is a provision in the bill that would defund Planned Parenthood for a year, a stipulation opposed by Republican U.S. Sen. Susan Collins of Maine.

Gardner did not provide a definitive answer on whether he supported the Planned Parenthood provision when asked about it several times last week.

Meanwhile, Democrats and liberal advocates have ramped up their opposition to the bill, saying it would do significant harm to Colorado, a state that largely has embraced the Affordable Care Act — both on a policy level and in recent public polling.

“This bill is awful, and Gardner knows it,” said Ian Silverii, executive director of ProgressNow Colorado​, in a statement. “The public wants this madness to end. They want Obamacare fixed, not repealed.”

The most obvious impact of the Senate proposal on Colorado would be its effect on the state’s Medicaid rolls. Because of the Affordable Care Act, Colorado expanded Medicaid to include an estimated 407,000 residents and — in the process — lower the number of Coloradans without health insurance from 15.8 percent in 2011 to 6.7 percent in 2015.

One effect of that decrease was a sharp drop to the cost of “uncompensated care,” the cost to hospitals for treating patients without insurance. In Colorado, that cost fell from $2.3 billion in 2009 to less than half that amount in 2015 to roughly $1.1 billion.

The Senate bill would phase out the Medicaid expansion starting in 2021. Republicans have raised concerns about the long-term cost of Medicaid spending.

Gardner said he was working on revisions to the health care bill that would address on the topic of Medicaid, though he provided few details.

“We’re looking at some ideas on Medicaid,” Gardner said. “We’re trying to see what support we have.”