President Trump edged into the bully pulpit Tuesday in his address to a joint session of Congress with a fresh push for Republican-driven health care reform, marking a late arrival into a fray that for weeks has engulfed GOP lawmakers at fiery town-hall meetings.

In his remarks in the House chamber, Trump devoted only a few minutes of his sprawling speech to one of his biggest policy priorities. But congressional Republicans hope the president’s remarks will herald the start of a larger offensive by the White House to sell Americans on their proposed reforms and persuade uncertain lawmakers to back legislation.

“Obamacare is collapsing, and we must act decisively to protect all Americans,” Trump said. “Action is not a choice — it is a necessity.”

Republican leaders in Congress are already deep into the process of developing a legislative path forward. “We’ve had a bicameral working group for more than a month, so you have Senate members and House members working together to produce a draft,” Tennessee Sen. Lamar Alexander told reporters Tuesday.

But, lawmakers believe, it will soon be incumbent on the president to explain the ultimate proposal and rally Americans behind it — to say nothing of their skeptical colleagues whose votes will be crucial to its success.

“I absolutely believe the bully pulpit will work, and I’ve been on the record as saying it may be up to President Trump to sell the ultimate plan to some fence sitters,” said New York Rep. Chris Collins, who was among Trump’s early supporters on Capitol Hill.

South Dakota Sen. John Thune, a member of the Republican leadership, echoed Tuesday that it “would be really helpful for the president to engage as much as possible.”

“It's helpful to us up here for him to weigh in, and I think he will do that,” Thune said. “We expect to hear from him on tax reform, we expect to hear from him on health care, and a whole range of other issues.”

By default, the president enjoys a much larger platform than any member of Congress — and Trump perhaps more so than any of his predecessors. He has established himself as a prolific Twitter user, and his knack for messaging and branding helped to win him devoted supporters in the presidential election. In his business career before that, his self-promotion and salesmanship were renowned.

Those qualities have been less pronounced in his young presidency, however. And Trump has so far been withdrawn from the roiling fight on health care as it has unfolded in congressional town halls across the country, with constituents demanding guidance and answers from their lawmakers on changes to come.

Moreover, Trump has seemed taken aback at the depth of policy challenges facing lawmakers on health care. “I have to tell you, it’s an unbelievably complex subject,” the president said Monday. “Nobody knew that health care could be so complicated.”

Trump doesn't need to remind his own party’s leaders, who have struggled in recent weeks to explain their plans to nervous, angry constituents, and to coalesce Republican support behind a single proposal.

Even before Republicans have officially rolled out their proposed reforms, some party lawmakers have this week drawn a line in the sand — insisting they will not support any measure short of a full repeal, nor any replacement that would comprise tax credits in place of a mandate. This group includes the chairmen of the Republican Study Committee and Freedom Caucus, two influential conservative groups in the House.

“I think we have the votes now to tell leadership what we want to do,” Kentucky Sen. Rand Paul, one of the Republicans pushing for a more conservative approach, told reporters Tuesday. “... We’re a force to be reckoned with.”

Trump has so far taken a laissez-faire approach to the unfolding policy debates over health care, and he did not wade far into policy details in his remarks to Congress on Tuesday — except to vouch his support for a plan comprising tax credits to purchase insurance. White House Press Secretary Sean Spicer explained to his congressional counterparts in a private meeting earlier in the day that the president would deliberately focus on “the broad contours” of the issue, Politico reported.

However, Rep. Tom Cole warned in a New York Times op-ed Tuesday that Trump "will need to do more than merely wait upon a Republican Congress to produce the legislation he has championed. He must become an active participant in the legislative process."

President Obama, in his own health care fight in the first year of his presidency, initially thought he would have the same luxury of letting Congress take the lead on the hairy details. But he ultimately learned that the legislative process benefits from nudging by the executive branch.

During the summer of 2009, as Obama’s health care proposal met with roadblocks on Capitol Hill, he leaned in and activated his bully pulpit — holding health care town halls and engaging more aggressively with the media.

“We will be weighing in more definitively, and you will see him out there,” White House budget director Peter Orszag told The New York Times in June 2009.

Trump, of course, has not always been a consistent or welcome messenger on behalf of the Republican Party, a dynamic that might water down enthusiasm for his engagement on health care and other front-line legislative issues.

"I've been pretty candid with him and all of you that I'm not a fan of the daily tweets," Senate Majority Leader Mitch McConnell offered earlier this month, responding to a daily flap.

But the president has also conceded a degree of self-awareness on this front, suggesting Tuesday that he has barely made a passing grade in communicating his agenda to Americans, by his own standards.

"In terms of messaging, I would give myself a 'C' or a 'C-plus,’” Trump told Fox News.

If Trump is to improve on that rating, health care might be his biggest test. Not only will he need to explain the thrust of the Republican substitute for Obamacare, but lawmakers say he will need to highlight the urgency of the issue as Congress marinates on it.

“The American people need to understand what thin ice we’re on right now if we don’t make a change,” said Sen. Thom Tillis, a North Carolina Republican.

A recent NBC News poll shows a more muddied public sentiment, with most agreeing some change to the Affordable Care Act would be positive, but with less agreement about what that would look like. Thirty-one percent of people polled said they have a “great deal” or “some” confidence in a Republican plan to improve the existing law.

But some Republicans caution that it is still early, trusting that more concerted outreach efforts are on the horizon in coming weeks as the party’s policy plans come into sharper focus.

“We’re not yet to the point where we have just one idea that we’re trying to push,” said Texas Sen. John Cornyn, another member of Republican leadership, “but when that time comes, I think the president’s role is going to be indispensable.”