As his administration attempts to repeal and to replace Obamacare, President Donald Trump sought to try his salesman skills on Republicans sceptical of his new healthcare bill and prod them into supporting it in a key vote later this week.

Trump spoke to House Republicans early on Tuesday 21 March and picked out members of the Republican Freedom Caucus, made up of hard-core conservatives who support the Tea Party movement. President Trump urged them to support the bill because "a loss just isn't acceptable," a source inside the meeting told CNN.

"He told us if we don't pass this bill on Thursday, it will put everything in jeopardy that he wants to do, his agenda," Rep. John Duncan (R-TN) also told The Hill after the meeting ended.

Some of the caucus' members have decried Trump's healthcare proposals are too soft and similar to the Affordable Care Act known widely as Obamacare.

An analysis by the Congressional Budget Office (CBO) of the Republican designed American Health Care Act (AHCA) last week, however, projected that some 24 million Americans would be worse off under the bill.

The bill also targets cuts to care for older, and poorer Americans while giving tax breaks to the wealthiest 1% of their countrymen.

Trump kicked off the meeting on Tuesday by talking about how big the crowd of his supporters was at a rally he held in Lousiville, Kentucky, the night before. "We won't have these crowds if we don't get this done," he said. "I honestly think many of you will lose your seats in 2018 if you don't get this done."

Caucus chairman Mark Meadows later shrugged off the president's claims. "I serve at the pleasure of the people of western North Carolina, and when you serve at their pleasure, it's only those 750,000 people that can send you home," he told reporters after the meeting, adding he is still against Trump's proposals "because the bill we're currently considering does not lower premiums for the vast majority of Americans."

Other members of the Freedom Caucus also oppose the bill. Exactly how many of its 40 members stand against the legislation drafted by Republican House Speaker Paul Ryan and President Trump isn't clear. The bill faces a full vote to pass the House before heading to the Senate on Thursday.

Republicans need 216 votes to get the bill through and cannot withstand more than 21 defectors in their ranks. "We're gonna have a real winner. It was a great meeting...I think we'll get the vote on Thursday," Trump said as he left the meeting earlier.

House Republicans made a few changes to the bill late Monday in hopes it will win over some of their party members. They left a decision about whether to give more tax credits for health insurance to older Americans up to the Senate and added a provision that requires able-bodied people who get Medicaid assistance to be in work.

Many Republicans stand against the bill for other reasons. Conservative columnist Bill Kristol wrote on Twitter that the bill doesn't lower costs, improve insurance, increase liberty, or make healthcare better "so what's the point?"

House Speaker Paul Ryan sought to to show solidarity within the party as they prepare to vote for the bill. Trump, Ryan said in a press conference following the meeting, "is all in and we are all in to end this Obamacare nightmare."

US President Donald Trump (R) and Secretary of Health and Human Services (HHS) Tom Price (L) arrive to meet with congressional Republicans at the US Capitol in Washington DC 21 March 2017 Reuters/Jonathan Ernst