A Real Clear Politics average of leading polls finds Mrs Clinton with a decisive advantage, 44.1 per cent to 38.3 per cent.

The four most recent polls show Mrs Clinton with leads of 12, nine, five and six points.

In an ominous sign, Mr Trump is struggling to break away from Mrs Clinton in conservative states such as Arizona and Utah.

The former secretary of state looks poised to open up a big fundraising advantage over the property developer, as some conservative donors elect to help Republican senators save their seats rather than Mr Trump.

Appreciate the congrats for being right on radical Islamic terrorism, I don't want congrats, I want toughness & vigilance. We must be smart! — Donald J. Trump (@realDonaldTrump) June 12, 2016

In the past week, many Republicans have disassociated themselves from Mr Trump.

Maryland governor Larry Hogan said he does not plan to vote for him on November 8.

Ohio governor and presidential candidate John Kasich said he was not ready to back Mr Trump.


Republicans Richard Armitage, the deputy secretary of state under George W. Bush, and former Minnesota governor Arne Carlson reportedly said they will vote for Mrs Clinton.

Regarding all of the discussion about the RNC Rules committee - see attached pic.twitter.com/RXNZSqbm0b — Sean Spicer (@seanspicer) June 17, 2016

Senate majority leader Mitch McConnell and other prominent Republicans on Capitol Hill have refused to answer media questions about Mr Trump's antics.

House Speaker Paul Ryan, who unenthusiastically endorsed Mr Trump, told NBC over the weekend that he did not necessarily expect other Republicans to back the presumptive nominee.

"The last thing I would do is tell anybody to do something that's contrary to their conscience," Mr Ryan said.

On Saturday, Mr Trump took a swipe at party loyalists resisting him, saying he would beat Mrs Clinton and "it would be helpful if the Republicans could help us a little bit".

General Election: Trump vs. Clinton, average of eight leading polls. Real Clear Politics

The July 18-21 Republican National Convention (RNC) in Cleveland is where Mr Trump is due to be officially crowned the party's nominee. It is shaping as a divisive affair.


A small group of conservative forces continue to mobilise in the hope of denying the real estate mogul the nomination.

The opposition forced RNC chief strategist Sean Spicer on Friday to dismiss chatter the party might change the rules to prevent Mr Trump being the nominee.

"Donald Trump bested 16 highly qualified candidates and received more primary votes than any candidate in Republican Party history," Mr Spicer said in a statement on social media.

"All of the discussion about the RNC Rules Committee acting to undermine the presumptive nominee is silly. There is no organized effort, strategy or leader of this so-called movement. It is nothing more than a media creation and a series of tweets."

While Mr Trump is deeply unpopular with most Americans, Mrs Clinton has popularity of challenges of her own.

Some 55 per cent of voters view her unfavourably.