Pushing to define Romney and respond to attacks from conservative groups, Obama spent nearly $58 million in June, far more than any previous candidate has spent at this point in the campaign. Romney’s team, by comparison, spent $27.4 million.

The numbers, in disclosures filed Friday with the Federal Election Commission, underscore how rapidly the fundraising contest has been transformed since Romney was all but assured the Republican nomination in April with little money remaining from a brutal primary fight.

Obama, whose fundraising juggernaut in 2008 became political legend, has had a harder time raising money this time and has been outraised by Romney for two straight months. The presumptive Republican nominee and affiliated party committees had $170 million cash on hand at the end of June, compared with $147 million for Obama and the Democrats.