WASHINGTON — President Donald Trump has called for bipartisan support for an overhaul of the Affordable Care Act, but his own party was divided on the issue.

In his first speech to a joint session of Congress, Trump asked Republicans and Democrats “to save Americans from this imploding Obamacare ­disaster.”

Reiterating his campaign rhetoric, the president asked the House and Senate to repeal and replace the ACA with reforms that expand choice, increase access, lower costs and provide better care. But he was short on specifics after acknowledging a day earlier that health care policy was “an unbelievably complex subject.”

President Donald Trump

Conservative Republicans, meanwhile, balked at proposed tax credits to help consumers purchase insurance. The credits could be higher than federal income taxes for some low-income households, which would make them a new entitlement, the critics charged.

Refundable tax credits are another way of saying subsidies, commented Sen. Rand Paul (R., Ky.). Paul and fellow GOP senators Mike Lee of Utah and Ted Cruz of Texas said in coordinated tweets that they opposed “Obamacare Lite.”

Prior to Trump’s speech, Republican leaders issued draft legislation revoking much of the ACA within a few years. The proposed bill would expand health savings accounts for individuals along with boosting tax credits, while cutting federal spending on subsidies and Medicaid and all but eliminating the employer and individual mandate to have health ­insurance.

The possibly imminent introduction of a replacement bill was seen as a way to jump-start the effort to fulfill Trump’s campaign promise for early action. But passing the legislation would require limiting Republican defectors to two Senators and 22 House members, assuming Democrats unite in ­opposition.

One key Republican, Rep. Mark Walker of North Carolina, said he could not back the GOP proposal. Walker, who chairs the Republican Study Committee, which has 170 members, told Bloomberg that he would advise that his fellow members also reject the plan. “The bill contains what increasingly appears to be a new health insurance entitlement with a Republican stamp on it,” he said.

House Minority Leader Nancy Pelosi of California said on ABC’s “This Week” that Republicans lacked the votes for a repeal.

The possibility of dramatic congressional action was spurred in part by angry constituents who confronted legislators at town hall meetings over the potential loss of health coverage. Also, polls have showed increased support for the ACA, leading some GOP policy makers to adopt a “now or never” approach.

Douglas Holtz-Eakin, a Republican economist and health analyst, said GOP legislators had boxed themselves into a corner and had to act.

Persistent questions surrounding the repeal effort include how replacement legislation would handle Medicaid, whether millions of people might lose insurance and how to fund the new plan.

The nonpartisan Congressional Budget Office said the GOP plan would be costlier than Republicans hoped and would cover fewer people than the ACA. The analysis was revealed by lobbyists speaking on the condition of anonymity to discuss conversations with congressional aides.

For many Republican lawmakers, those problems are outweighed by promises they’ve made for years to overturn Obamacare. House Speaker Paul Ryan (R., Wis.) reiterated Republicans’ commitment to an overhaul. “I think the Democrats got too far ahead on their ideology and they gave us a system where a government runs health care,” he said on NBC’s “Today.”

“They gave us a system where costs went up, not down,” he said. “They gave us a system where choices went away. They gave us a system where people lost the health care plans that they liked that they chose. That violated all the promises that were made, that were given when Obama­care was sold to the American ­people.”

“Now we have a collapsing marketplace,” he added. “We really believe we are in a rescue mission here to step in and prevent this collapse from ­occurring.”

But former speaker John Boehner said earlier that the ACA would not be overturned. “I shouldn’t have called it repeal and replace because that’s not what’s going to happen,” he said. Republicans are “basically going to fix the flaws and put a more conservative box around it,” he said.

Senate Minority Leader Chuck Schumer (D., N.Y.) told reporters that Republicans had yet to win any Democratic support for repeal, calling the odds against it “very high.”

Trump said in his speech that the individual mandate requiring every American to get health insurance “was never the right solution for America. The way to make health insurance available to everyone is to lower the cost of health ­insurance, and that is what we will do.”