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The biggest change has occurred among Republicans: In May, half of the GOP insiders thought the criticism was ineffective. Now, only 12 percent of Republicans think Obama's Bain scrutiny won't work -- 67 percent think it is somewhat effective and 22 percent say the criticism is highly effective.

Democrats were initially more bullish about the president's tactics, but their opinions have also swung in Obama's favor. Fifty-four percent of left-leaning insiders thought the party's attack was highly effective two months ago, while nearly 80 percent of them think so now.

Romney's tenure at the private equity firm has long been a subject of attack, dating back even to the Republican presidential primary. But driven by an aggressive ad campaign from the president's allies and questions about when he left the company, Romney's business background has emerged as one of the race's major stories.

And, according to Republican and Democratic insiders, it's been egged along by a thus far stuttering response from the Romney campaign, whose defense of his tenure has consisted largely of decrying Obama's attacks as misleading and unfair.

"It's effective only because the Romney campaign has been so bad at responding," said one Republican insider.

Added another: "The message is not particularly effective, but the fact that Romney seems totally incapable of responding is. Didn't they know this was coming since about 1994?"

Obama initially faced backlash within his own party about his attacks, but Democrats now say the president's campaign is smartly defining Romney early on even before many voters begin paying close attention.

"Great summertime strategy," said one Democratic operative. "Rough him up, keep the campaign off balance, start bi-partisan pundit class carping; all the while, knowing there is a lot more to the campaign that this flap."

Said another Democrat, "Team Obama ignored the East Coast bedwetters and the super-rich donor whining and ran with Bain in the battleground states, and it is working."

The urgency behind the president's broadsides has only increased as the country's stalling economic recovery soften his own approval ratings. Attacking Bain, coupled with demanding Romney release more of his tax returns, has focused the media's attention on the GOP contender's background instead of Obama's own record.

"Just look at the narrative," a Democratic insider said. "Instead of talking about weak June jobs report, the media and voters are focused on Bain, Swiss bank accounts and Romney not releasing his tax returns. Remarkable."

Still, some Republican remain optimistic that even if Romney has had a difficult few weeks, the race's fundamentals will eventually take hold again to their candidate's advantage.