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President Obama today will continue his record-smashing fundraising schedule with six events in two states, tying the number for most fundraisers attended in a single day of his re-election campaign. Obama will raise north of $3.6 million for the Obama Victory Fund in Baltimore and Philadelphia, according to figures provided by the campaign.

The latest round of money events - with several more scheduled for New York City on Thursday, including a star-studded reception at actress Sarah Jessica Parker's home - underscores the unprecedented amount of time the president is spending on the money trail.

In the first 12 days of June, Obama has attended 21 fundraising events. All told, he has now attended 163 re-election fundraisers for his campaign and the Democratic Party - almost double the number George W. Bush attended in his entire first term (86) and more than any other president in history.

President Obama noted in an interview Monday that his busy schedule prevented him from campaigning in Wisconsin for Tom Barrett ahead of the recall vote. "The truth of the matter is that as president of the United States, I have a lot of responsibilities," he told ABC's Green Bay, Wis., affiliate WBAY.

Those "responsibilities" in the days before and after the vote included a public schedule dominated by fundraisers: six in Minneapolis and Chicago three days before the election; three in New York City on the eve of the election (including a flight on Air Force One with Bon Jovi); and five more the day after Barrett lost.

And a growing number of the money events are closed to the press, despite Democrats' criticism of Mitt Romney for the same. In June alone, Obama has held six private roundtables with deep-pocket donors who each paid more than $40,000 for face time and influence with the president.

Presidential historians and political scientists tell ABC News the fundraising spike is due to the rising costs of campaigns, contribution limits that are low relative to the cost of campaigns and the abandonment of the public financing system. They also point out that Obama is under pressure to compete against pro-GOP outside groups that have pledged hundreds of millions of dollars to defeat him.

"Carter, Reagan, Bush 41, and Clinton all accepted public funding at both the nominating and general election stages - and this is key to the small number of fundraisers they attended," said U.S. Naval Academy political scientist Brendan Doherty. "They were bound by the spending limits that came with public funding." But not so for George W. Bush and Barack Obama.

Even while Obama's fundraising frenzy can be explained, it still means significant expense to taxpayers for costs of presidential travel and security that are not reimbursed by the campaign.

For example, Air Force One costs $180,000 per hour to ferry the president around the country. But the Obama campaign only reimburses the government for a fraction of that amount.

The campaign uses a complicated formula that's based on what it would cost to charter a 737 to make the same flight, according to the White House. It's a price significantly less.