President Obama warned supporters Tuesday that Republicans have boiled down their campaign against him to a single phrase that can fit into a 140-character Twitter message and unfairly blames him for the nation’s ills.

“Because folks are still hurting right now, the other side feels that it’s enough for them to just sit back and say, ‘Things aren’t as good as they should be, and it’s Obama’s fault,’ ” the president said during a campaign fundraising appearance at a home in a Baltimore suburb.

“You can pretty much put their campaign on a tweet and have some characters to spare,” he said.

The quip neatly summed up his campaign’s concern that Republicans have begun to make headway in their attempt to pin the economy’s sluggishness on his administration, and it reflected the urgency with which Obama is hoping to turn the corner on nearly two weeks of dismal economic and campaign news.

The president’s GOP rivals quickly fought back, taking to — what else? — Twitter to mock Obama’s remarks, using the hashtag “#characterstospare.”

“Unemployment at 8.2% for a record 40 straight months. #characterstospare,” the Republican National Committee wrote, even though the national unemployment rate dipped to 8.1 percent in April before rising to 8.2 percent last month.

“Where are the jobs? — How many #CharacterstoSpare do I have?” tweeted Brendan Buck, spokesman for House Speaker John A. Boehner (R-Ohio).

The combative mood underscored the high stakes as Obama set out on a whirlwind fundraising tour Tuesday, seeking to remain financially competitive with Republican presidential candidate Mitt Romney.

In Philadelphia later in the day, Obama sought to counter the Republican message even more forcefully, saying GOP leaders drove up the deficit — and then moved “suddenly to get religion” on spending.

“They ran up the tab and are trying to pass off the bill to me,” Obama said to a crowd of about 500 at the Franklin Institute, a science museum.

“Let me tell you something,” he added, to cheers. “The two presidents with the least growth in government spending in the modern era happen to be two Democrats named Barack Obama and Bill Clinton. It wasn’t the other guys.”

Obama’s six fundraisers in Baltimore and Philadelphia were expected to net his campaign at least $3.6 million and take his total number of such events for the 2012 cycle to 160, according to Mark Knoller of CBS News, who keeps a variety of presidential statistics. That’s more than double the pace of President George W. Bush at this point in his 2004 reelection bid.

The intensity reflects a long-held concern among Obama advisers that Romney, along with a number of GOP super PACs, could raise more money than Democrats. That concern turned into outright worry last week when Romney released figures for May showing that he and GOP groups had outraised Obama and Democrats for the first time in the cycle.

Obama also is trying to turn around an increasingly negative narrative about his stewardship of the economy and his prospects for reelection. Starting with a dismal jobs report for May, Obama has been beset for days by bad news and missteps, including saying in a news conference Friday that “the private sector is doing fine.”

At the first event Tuesday, at a private home in Owings Mills, Obama said that “you’ll never see a sharper contrast” between the two parties than in the upcoming election.