"President Obama has had three disappointing months, but he's holding his own," said Kristol on Fox News Sunday, citing polls which show him even with or leading Romney despite a series of weak jobs reports. "If I were in the Romney campaign that would worry me."
He pointed to a Fox News poll showing Romney performing worse than Obama on the economy, which voters rank as the most important issue this election.
"I think the Fox News poll actually has the key to what the problem is for the Mitt Romney campaign. Do you think Barack Obama has a clear plan for improving the economy or not? Yes, 41; no 53. It's not great for an incumbent president. The economy is slow. And you are only at 41-53," said Kristol.
"Do you think his challenger, Gov. Romney, has a clear plan for improving the economy or not? Yes, 27; No, 55," he continued.
"I don't think you can beat an incumbent president, even if the economy is slow, if 27 percent of the voters think you as the challenger don't have a clear plan for improving the economy," Kristol said.
Romney's team has faced a barrage of criticisms from conservatives in the last week.
On Thursday, the editorial board of the Wall Street Journal blasted the campaign as "politically dumb" for its response to the Supreme Court ruling upholding Obama's healthcare reform law.
Senior Romney adviser Eric Fehrnstrom said the candidate viewed the individual mandate as a penalty early last week, undercutting GOP attempts to characterize the health law as a massive tax increase.
But Fehrnstrom was contradicted by Romney days later, when the former Massachusetts governor said the mandate was a tax.
Media mogul Rupert Murdoch, CEO of NewsCorp., also criticized the Romney campaign in a tweet last week saying that Romney would lose the election unless "drops old friends from [his] team and hires some real pros."
Kristol on Sunday acknowledged that many conservatives were "frustrated."
"I think what a lot of people would like to see -- a lot of people hope Mitt Romney wins the presidency in November, which I certainly do, is like to see him stand up and say I have a plan and I am going to aggressively address these problems and fix the economy," he said.
"They're very risk-averse, but being risk- averse can be risky," he cautioned.