US President Donald Trump has claimed his party "essentially repealed Obamacare" by passing a tax bill that rescinds a key component of his predecessor's health care legislation.

The Republican tax bill repeals the health insurance mandate that forms the core of the Affordable Care Act, also known as Obamacare. Mr Trump claimed the repeal would cripple Obamacare – something he and his party have long promised to do.

“When the individual mandate is being repealed that means Obamacare is being repealed," Mr Trump told reporters at a Cabinet meeting. "...We have essentially repealed Obamacare and we will come up with something much better.”

The individual mandate requires all Americans to have health care coverage, or pay a penalty fee. The mandate encourages healthy people to buy insurance, which helps to keep premiums lower.

Without the individual mandate, the number of uninsured Americans would increase by 4m in 2019 and 13m in 2027, according to the Congressional Budget Office. Premiums are also expected to increase by about 10 per cent.

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The Republican tax bill repealing the mandate passed both the House and Senate earlier this week. It returned to a final vote in the House on Wednesday, after the Senate made several minor, last-minute adjustments. The bill now goes to Mr Trump to be signed.

The bill's passage is expected to be the first major legislative achievement of the Trump administration. It will also be a welcome win for Republicans in Congress, who tried and failed to repeal Obamacare several times this summer.

Mr Trump, however, claimed he did not play up the mandate repeal until now, for fear that it would be misrepresented by the media.

“Now that it’s approved, I can say that," he said on Wednesday.

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The Republican tax bill does not fully repeal Obamacare. The Obama-era Medicaid expansion will stay in place, as will protections for women, people with pre-existing conditions, and other vulnerable populations.

Americans will also still be able to buy health insurance through the ACA exchanges – though approximately 4.5m fewer people did so this year than last. This year's exchanges offered fewer options and higher premiums than in the past, and the Trump administration slashed the amount of time Americans had to enroll.

In a statement celebrating the passage of the tax bill, Mr Trump lauded the "great spirit of optimism sweeping across our land".