Washington - The Republican Party of the United States is taking steps to close ranks behind its second candidate, Donald Trump, to prevent the victory of the probable Democratic challenger, Hillary Clinton.

Although many Republicans have refused to support the leading candidate, others, like Senator John McCain, have called on their colleagues to join forces and listen to the voters who have already expressed their intention to vote for the New York tycoon.

Trump himself admitted in an interview with ABC's program "This Week" on Sunday that it would be better if the party were united, although he did not rule out that he might get support from Democratic voters against Clinton.

The businessman belittled the problems he is facing to unite the party's ranks behind his candidacy, although members of his campaign consider that it is happening faster than they expected.

On Sunday, Trump also appeared in NBC's program "Meet the Press", where he criticized former Presidential Candidate Mitt Romney, whom he described as ungrateful, after he supported him in 2012 and who is refusing to support him now.

Trump is expected to meet in Washington on Thursday with the speaker of the House of Representatives, Paul Ryan, who has not decided yet to support him, and with the chairman of the National Republican Committee (NRC), Reince Priebus.

He will also meet with a group of Republican leaders of the House, as part of his efforts to bring the party together, although prominent politicians like ex Florida Governor Jeb Bush and members of the family clan refuse to support him in November's elections.