WASHINGTON (Reuters) - U.S. President Donald Trump backed the use of tax credits to help people purchase health insurance in a speech to Congress on Tuesday, the first time he signaled support for a key component of House Republican proposals to replace Obamacare.

Republicans, who control the White House and Congress, are united in their opposition to former Democratic President Barack Obama’s signature 2010 healthcare law, but have so far failed to agree on the details of how to replace it.

“We should help Americans purchase their own coverage, through the use of tax credits and expanded Health Savings Accounts,” Trump said. “But it must be the plan they want, not the plan forced on them by our government.”

Democrats are ardently opposed to tampering with Obamacare, which provided coverage to millions of previously uninsured people.

A draft Republican replacement for Obamacare would include an age-based monthly tax credit that Americans who do not get health insurance through their employer could use to buy coverage and take from job to job.

Some Republicans have voiced resistance to that plan.

The president’s comments were also a nod to health insurers - whom Trump met with on Monday - who say tax credits are necessary to keep people in the market.

“The fact that he used the word tax credits is a signal to congressional Republican ranks” that he supports their proposals, said Tom Miller, a resident fellow in health policy at the American Enterprise Institute think tank.

Trump also said Americans should be able to buy insurance across state lines, a proposal favored by health insurers because it would enable them to offer plans in states with fewer regulatory hurdles.

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Trump said state governors should be given resources and flexibility on Medicaid, the government health insurance program for the poor, and ensure that “no one is left out.” That appeared to be an attempt to ease concerns from the more than 30 governors who expanded Medicaid coverage under Obamacare.

But Trump offered few details on how he would reconcile House Republican plans to unwind the expansion of Medicaid with promises to maintain coverage for those who gained health insurance under Obamacare.

He also reaffirmed that those with pre-existing conditions should have access to coverage but did not say how that would be accomplished.