(CNN) - The senior strategist for President Barack Obama's re-election team said he's "not surprised" his campaign raised less money last month than Republican rival Mitt Romney.
David Axelrod attributed Romney's May haul of $77 million to the end of the Republican primary season, allowing the presumptive GOP nominee to shore up cash that was previously going to a crowded field of contenders.
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"You pick up all the money that you couldn't raise in the primary from Republicans who were supporting other candidates," Axelrod said on CNN's "The Situation Room with Wolf Blitzer." "So we anticipated this."
Romney's fundraising totals came from a joint effort between Romney for President, Romney Victory, and the Republican National Committee. The figure marked a big jump from April, when he took in $40.1 million.
Since the beginning of April, Romney's rivals Rick Santorum and Newt Gingrich have dropped out of the race. The former Massachusetts governor also crossed the 1,144 delegate threshold for the August convention, essentially clinching the GOP presidential nomination.
Obama's campaign, meanwhile, announced Thursday it raised $60 million in May, an amount also divided between the re-election campaign, the Democratic National Committee and affiliated Democratic state parties.
While Romney's numbers were higher in May, the Republican effort said they ended May with $107 million in the bank. Obama's campaign did not disclose their cash on hand for May, though they ended April with $115 million.
Responding to the Romney fund-raising announcement, Obama campaign press secretary Ben LaBolt tweeted: "Reminder on RNC/Romney camp fundraising: 1st month joint committee was in existence, so all their primary donors wrote their maxout checks."
Romney and the RNC joined fund-raising forces beginning May 8.
- CNN's Kevin Liptak and Ashley Killough contributed to this report.