The Republican Party under Donald Trump has become a “right-wing extremist party”, Bernie Sanders has said.

The veteran US senator was speaking as the Republican leadership attempted to convince senators to vote to repeal the Affordable Care Act, widely known as Obamacare, which extended health insurance coverage to millions of Americans.

Some Republican senators said they would only vote for the plans if they were assured they would never become law. In the end the Senate voted narrowly against repeal.

Mr Sanders told MSNBC’s Chris Hayes the attempt to scrap the Act is a sign the Republicans are now following the ideology of the Koch brothers – two billionaire US businessmen who have funded a range of conservative and libertarian causes.

“The Republican Party is now, in fact, a right-wing extremist party", Mr Sanders said.

He added: "As you know, the Koch brothers do not want to see cuts to see social security or Medicare or Medicaid – they want to eliminate those programmes. They want to eliminate every federal programme passed in the last 80 years that was designed to protect working families or children or the elderly or the sick of the poor. That is their agenda and this is the beginning of their agenda”.

The Koch brothers have made the repeal of Barack Obama’s signature healthcare legislation a fixture of their political agenda.

They have previously criticised Republican efforts to dismantle Obamacare as not going far enough, especially when it comes to cutting Medicaid.

They also donated to more than 350 Republican lawmakers in 2016, and helped earn Vice President Mike Pence a place on the ticket with Mr Trump.

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Mr Sanders warned that if Republican plans to repeal and replace Obamacare were successful, it would empower the brothers to further their agenda.

“If they are successful in whatever this thing turns out to be ... mark my words, they will be back to privatise Medicare within a few months, and then they will go after Social Security and the Veterans Administration,” he said.

The veteran senator, who ran against Hillary Clinton for the 2016 Democratic presidential nomination, described the Republican healthcare plans as an “abomination”.

“What we have here, which is not a laughing matter, is a disastrous piece of legislation that would raise premiums 20 per cent this year, 20 per cent on top of that and 20 per cent on top of that,” he said.