President Obama and top White House aides are waging a behind-the-scenes push to win over skeptical big-dollar donors — whose early money is needed to help fund a dramatic summertime expansion of his battleground-state machinery.

Campaign officials are working to broaden Obama’s network of “bundlers,” the well-connected rainmakers tasked with soliciting big checks from wealthy donors, while seeking to preserve the aura of a grass-roots movement by luring back the kind of small Internet donations that helped shatter fundraising records four years ago.

To do so, Obama and his aides are leveraging every asset available to a sitting president — from access to top West Wing officials to a possible food tasting with the White House chef.

Much of the fundraising in recent weeks has occurred at targeted events designed to appeal to specific groups, many of which have expressed frustration with administration policies, including Jews, gays and business leaders. Obama has attended 28 fundraisers from coast to coast — a pace that could continue, or even accelerate, over the next several months.

The West Wing charm offensive shows how Obama’s White House, which has eschewed Clinton-style traditions of feeding donor egos with Lincoln bedroom overnights and frequent phone calls from the president, is adjusting itself for a campaign that needs to overcome low approval ratings and a sour economy.

“They were more skewed toward their base,” said Steven Green, a former Samsonite chief executive and donor to Bill and Hillary Clinton’s campaigns who hosted an Obama fundraiser in Miami this month. “Now they realize that there is this large group of donors out there, and for better or for worse, they need to cater to them. To be frank, I think it’s somewhat new to them, and they’re not quite sure how to address that donor base. [The donors] are pretty high-maintenance.”

The push comes as Obama’s campaign has roared to life in recent weeks and strategists prepare for a summer of staff hirings and field office openings across key battleground states.

It is an unusually early move to establish the ground-level infrastructure that past campaigns typically put in place in the final months before an election.

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