President Obama’s resurgence in a new Washington Post-ABC News poll — his 49 percent job approval rating is as high as its been since May — is built in no small part on a growing sentiment in the electorate that he is fighting for the middle class.

Asked who they trust more to protect the middle class, 50 percent of respondents chose Obama while just 35 percent named “Republicans in Congress”.

President Barack Obama walks from the podium after speaking during the news briefing at the White House, Tuesday, Dec. 20, 2011, in Washington. (AP Photo/Carolyn Kaster)

Dig deeper into the numbers — and thanks to the crack Washington Post polling department for helping us do just that — and it’s clear that the President’s middle class messaging is resounding in the critical center of the electorate.

Among independents, 49 percent trust Obama more to look out for the middle class while 32 percent side with congressional Republicans. Self described moderates opt for Obama by a wide 58 percent to 26 percent margin.

People who earn between $50,000 and $100,000 — roughly the median household income for those defined as “middle class” — choose Obama 50 percent to 36 percent. Those making under $50,000 give Obama an 18-point edge while the president fights to a statistical draw — 41 percent Obama, 42 percent Republicans — among those making more than $100,000.

Obama campaign advisers credit his more populist pitch — beginning with the rollout of the American Jobs Act and continuing through his ongoing battle on the payroll tax extension — for the improved numbers on the question of who is fighting for the middle class. (It’s not by accident that the White House has installed a countdown clock to the expiration of the payroll tax cut in the briefing room.)

“He actually believes in his core that restoring middle class security is the greatest challenge of our times, and everything he does is centered on that premise,” said Stephanie Cutter, a senior adviser to Obama’s re-election campaign.

As we have written before, winning the battle for the middle class is no small deal when it comes to the 2012 election. Those making between $30,000 and $100,000 have one of the key swing groups over the past four elections.

This chart tells the story:

The politics are simple. Win voters who make between $30,000 and $100,000 and you are well on your way to winning a national election. President Obama isn’t there yet but the latest numbers in the Post-ABC poll have to cheer his supporters.