History mandates presidential candidates release tax returns, but not how many

— Updated

No law requires presidential candidates to release their tax returns, but history does. President Obama’s re-election campaign is pressuring their Republican challenger Mitt Romney to release more of his tax returns. He has released one year, and one estimate's worth thus far. That should suffice, says the Romney camp.

When then Sen. Barack Obama ran against Hillary Clinton in the 2008 Democratic primary, his campaign similarly pressured her to release tax returns. A month after Obama released six years of returns, Clinton followed suit. The 2008 Republican nominee Sen. John McCain released two years of tax returns that year as well.

Going back to 1996, Republican Sen. Bob Dole released 30 years of tax returns ahead of the election, and in 1992 Bill Clinton released 12 years of tax returns (although critics said it wasn't enough). On and on it goes: Michael Dukakis released five years of returns when he ran in 1988, and George H.W. Bush forced Ronald Reagan's hand as both released their returns in the lead-up to the Republican nomination in 1980.

PolitiFact found only seven presidential or vice president candidates since 1976 have refused to release any tax returns. Romney is not among them, though he was in 2008. Those seven include five Republicans, one Democrat, and one Green Party: Jerry Brown, Pat Buchanan, Mike Huckabee, Steve Forbes, Rudy Giuliani, Richard Lugar, Ralph Nader.

Many have pointed out that it was George Romney (Mitt's dad) who started this trend when he released 12 years of tax returns in November 1963, a full year prior to the 1964 election, saying one year just wouldn't be enough.

And that's where the debate is centered now. While history demands that presidential candidates release their tax returns to the public in a sign of transparency, the record is less clear when it comes to how many years are necessary to establish some semblance of good faith.

The problem for Romney is that the media, his main challenger (Obama), and the public have remaining questions over his wealth and earnings that were not answered through the release of one tax return. It's likely he'll be forced to reveal more before November.