At a campaign rally in Florida, he said the Obama campaign had been "reduced to petty attacks and silly word games".
Hours earlier, Mr Obama decried Mr Romney for shifting his positions as election day draws nearer, saying the Republican suffers from "Romnesia".
The two meet for their final debate, on foreign policy, in Florida on Monday.
Mr Romney and the Republicans are continuing to focus on the Obama administration's handling of a deadly attack in Benghazi, Libya, in which four Americans including the US ambassador were killed.
The incident provoked a flashpoint during Tuesday's second debate, and is likely to be hotly debated again in Boca Raton.
'Romnesia'
Friday's campaigning saw both candidates make one major stop each: Mr Obama in the Washington DC suburb of Fairfax, Virginia, and Mr Romney in Daytona Beach, Florida.
Mr Obama told supporters that Mitt Romney was now only becoming more moderate as the election got closer.
"He is forgetting what his own positions are and he is betting that you are too," Mr Obama said, giving his rival's "condition" a crowd-pleasing name: "Romnesia".
The president renewed his pitch to women voters, arguing that "you don't want someone who needs to ask for binders full of women," a reference to Mr Romney's description of how he recruited women for cabinet positions as governor of Massachusetts.
"You want a president who's already appointed two unbelievable women to the Supreme Court of the United States."
Former President Bill Clinton also campaigned for Mr Obama on Friday in Wisconsin.
Mr Romney, appearing later on stage with running mate Paul Ryan, described the Obama campaign as "the incredible shrinking campaign".
"Have you been watching the Obama campaign lately?" Mr Romney told supporters at the Dayton Beach bandshell. "They have no agenda for the future, no agenda for America, no agenda for a second term. It's a good thing they won't have a second term."
Mr Romney said the Obama campaign had been "reduced to petty attacks and silly word games".
