Romney says he’ll (maybe) release his tax returns in April. When did Bush, Obama, McCain & Kerry do it?

After being pressed by Rick Perry during Monday night's debate in Myrtle Beach, S.C., Mitt Romney said he would "probably" release his tax returns in April if he becomes the presidential nominee of the Republican Party.

Romney acknowledged on Tuesday that the tax returns will indicate that he pays an effective tax rate of "closer to 15 percent."

"If I become our nominee, and what's happened in history is people have released them in about April of the coming year, and that's probably what I would do," Romney said Monday.

Candidates are not legally required to release their income tax records, but recent history mostly--but not always--supports Romney's claim.

Four years ago as a presidential candidate, Barack Obama released his tax returns for the years 2000 to 2006 in late March, when he was in the middle of a competitive race for the Democratic nomination.

Facing pressure from Obama, Hillary Clinton followed on April 4. Later that month on April 18, John McCain released his records. By that time, McCain had already locked up the nomination.

Romney did not release his tax records during his 2008 campaign.

In 2004, John Kerry, by then the presumptive nominee of the Democratic Party, released his 2003 tax records in April, as did President George W. Bush, who released his information every year while in office.

Before becoming president, George W. Bush released his tax information while serving as governor of Texas, including his complete income tax statement from 1996, well before he was a candidate for higher office.

In short, Romney would not be all that unusual if he chose to wait until April to release his tax records. So why is he facing so much criticism?

1. Romney has never stated with certainty that he will release his records--and has said that he does not intend to. Romney's statements Monday night were the closest he has come to saying he would release his tax records. And they fell far short of a clear, "Yes, of course I will release them."

In December, Romney said he had no plans to release his returns. "Never say never, but I don't intend to do so," he told NBC News.

2. His opponents are ponying up. Perry has made his tax records public for years as the sitting governor of Texas, and Newt Gingrich said he plans to make his records public on Thursday.

3. Details on Romney's taxes could be highly interesting or controversial. Romney's wealth and extensive business ties—something he is running on—make his tax return an object of larger curiosity than an ordinary politician's 1040.

Democrats and some of his Republican opponents have painted Romney as out-of-touch, in part because of his personal wealth. His tax returns could offer these critics more fodder. The same goes for his tax rate. Like Warren Buffet, Romney is paying lower tax rates than many middle-class Americans.

And Romney's record at Bain Capital, a Massachusetts private-equity firm, has come under scrutiny. If tax records show that Romney continues to substantially profit from the company--as is almost certainly the case--critics will likely attempt to link Romney to decisions made at Bain after he was no longer leading the company.

4. Transparency: All recent presidential nominees have released their tax returns voluntarily. It would be very difficult for Romney to argue why the American people can trust him were he to stand alone as the candidate who would not disclose his tax records.

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• Romney does the math on his tax rate ('closer to 15 percent') and his jobs record at Bain

• Romney makes new overtures to social conservatives in South Carolina

• Candidates pile on Romney in South Carolina debate

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