The Friday offer from President Obama's campaign to Mitt Romney — that if the GOP presidential candidate releases his tax returns for the past five years, it won't attack him for not releasing more — was immediately rejected by the Romney campaign.

But the give-and-take keeps Romney on the defensive, and promises to keep the issue of Romney's taxes going for weeks to come.

In case you missed it, Obama campaign manager Jim Messina wrote an open letter to Matt Rhoades, his counterpart with the Romney campaign. An excerpt:

"Governor Romney apparently fears that the more he offers, the more our campaign will demand that he provide. So I am prepared to provide assurances on just that point: if the Governor will release five years of returns, I commit in turn that we will not criticize him for not releasing more — neither in ads nor in other public communications or commentary for the rest of the campaign."This request for the release of five years, covering the complete returns for 2007-2012, is surely not unreasonable. Other Presidential candidates have released more, including the Governor's father who provided 12 years of returns."

Rhoades essentially responded with "drop dead," although he used a few more words:

"It is clear that President Obama wants nothing more than to talk about Governor Romney's tax returns instead of the issues that matter to voters, like putting Americans back to work, fixing the economy and reining in spending."If Governor Romney's tax returns are the core message of your campaign, there will be ample time for President Obama to discuss them over the next 81 days."In the meantime, Governor Romney will continue to lay out his plans for a stronger middle class, to save Medicare, to put work back into welfare, and help the 23 million Americans struggling to find work in the Obama economy."See you in Denver."

Denver, of course, is the site of the first presidential debate on Oct. 3.

Both campaigns will likely find many supporters for their positions. Recent polls suggest voters are split on the tax return issue.

For instance, Gallup had a July poll indicating that 54 percent of those surveyed wanted Romney to release more tax returns; but 37 percent said he shouldn't. Among Republicans, that figure was 65 percent. A Quinnipiac University/New York Times/CBS News poll conducted in August of voters in Wisconsin, Colorado and Virginia showed similar results.

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