House Ways and Means Committee Chairman Rep. Kevin Brady, R-Texas, left, listens to the committee's ranking member, Rep. Richard Neal, D-Mass., on Capitol Hill in Washington, Wednesday, March 8, 2017, as the committee began markup of the long-awaited plan by Republicans to repeal and replace the Affordable Care Act. (AP Photo/J. Scott Applewhite)
House Ways and Means Committee Chairman Rep. Kevin Brady, R-Texas, left, listens to the committee's ranking member, Rep. Richard Neal, D-Mass., on Capitol Hill in Washington, Wednesday, March 8, 2017, as the committee began markup of the long-awaited plan by Republicans to repeal and replace the Affordable Care Act. (AP Photo/J. Scott Applewhite) Credit: J. Scott Applewhite

WASHINGTON — Republican leaders labored to rally a divided party behind their high-stakes drive to overhaul the nation’s health care system Wednesday, but faced opposition from pivotal industry groups. House Speaker Paul Ryan praised the proposal as “what good, conservative health care reform looks like” as lawmakers cast Congress’ first votes on the GOP legislation.

House leaders wanted to push the measure through two committees — Ways and Means, and Energy and Commerce — by week’s end. While that seemed likely, they hit resistance from Democrats who oppose the seven-year GOP effort to unravel former President Barack Obama’s health care law.

Outnumbered Democrats used the panels’ sessions for political messaging Wednesday, futilely offering amendments aimed at preventing the bill from raising deficits, kicking people off coverage or boosting consumers’ out-of-pocket costs. They even tried, unsuccessfully, to insert language pressuring President Donald Trump to release his income tax returns.

The pivotal challenge for Republican leaders was coming not from Democrats but from rebellion in their own ranks and from potent outside groups. If that upheaval should snowball and crush the legislation, it would be a shattering defeat for Trump and the GOP, so leaders were hoping passage by both House committees this week would give them momentum.

Just as ominous as GOP unrest was hostility from three organizations instrumental in the 2010 enactment of Obama’s overhaul: The American Medical Association, the American Hospital Association and AARP, the nation’s largest advocacy group for older people.

In words aimed at his own recalcitrant colleagues, Ryan, R-Wis., declared the legislation “is bold and it is long overdue. And it is us fulfilling our promises.” The last was a nod to campaign pledges by Trump and many GOP congressional candidates.

There were signs of growing White House engagement, and perhaps progress. Trump met at the White House late Thursday with leaders of six conservative groups that have opposed the GOP legislation, and several voiced optimism afterward.