This is what's fuelling Donald Trump's recent surge in the polls

A combination of factors appears to be behind Donald Trump’s surge in recent national polls, pulling the real-estate mogul into a dead heat with Democratic frontrunner Hillary Clinton.

The Manhattan billionaire on Monday overtook Clinton in the RealClearPolitics polling average for the first time. Trump holds a 0.2% lead over Clinton in what is the gold-standard of polling averages.

According to the surveys that have shown him narrowing the gap, here’s why: Trump is quickly consolidating the support of his party, while Clinton’s still locked in a gruelling primary battle.

An NBC News/Wall Street Journal poll released Sunday had Clinton holding a 3-point lead, an 8-point swing from the month before.

The survey showed Trump’s support among Republican voters shooting up from 72% in April to 86% in May. Now, just 6% of Republicans say they won’t support the presumptive Republican nominee in the fall, compared to 13% in April.

Meanwhile, Clinton’s support among Democrats was slightly below Trump’s number with his party. The former secretary of state had the support of 83% of Democrats polled as part of the survey, while 9% said they are not backing her.

More potentially concerning for Clinton: The NBC/WSJ poll found that just 66% of Democratic primary voters supporting Bernie Sanders, the Vermont senator challenging her for the nomination, said they would support Clinton against Trump.

Those numbers jibe with a poll released earlier this month conducted by Mark Penn, Clinton’s chief strategist during the 2008 campaign. The poll, conducted in late March, found that just 64% of Sanders supporters would vote for Clinton in the general election.

Another Sunday poll — from ABC News and The Washington Post — found almost identical splits to the NBC/WSJ poll in terms of Republican and Democratic support for Trump and Clinton.

Trump held a 2-point lead in the ABC/Post poll.

And that survey also broke down support by ideological bend as well as partisanship. The numbers didn’t look especially great for Clinton.

Clinton’s lead over Trump among self-identified liberal voters dropped from a 77% to 16% lead in March to a 69% to 24% lead in May.

The Democratic frontrunner also saw a dropoff in support among self-identified conservative voters, going from being the preference of 23% of respondents in March to 18% in May. Trump went from 69% to 74% in that same timeframe.

Clinton led the Manhattan billionaire by a 49% to 39% margin among voters who view themselves as moderates — but that also represented a 12-point drop from her March lead. On the partisan side, independent voters favoured Trump by a 48% to 35% margin, a massive swing from the 48% to 39% edge Clinton held in March.

Together, the polls displayed is both a growing subset of self-identified liberal and independent voters who are straying from Clinton in a matchup against the presumptive Republican nominee, while Trump is consolidating support among the GOP establishment.

They suggest that perhaps Clinton’s biggest challenge over the next few months could be rallying the same kind of consolidation from Sanders supporters and other traditionally Democratic voters.

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