Out of the mouths of Bains. TPM:
When the it comes to the contentious topic of Mitt Romney’s tax returns, the Romney campaign has invoked precedent, defending their decision to release just two years worth of returns as the standard set by the campaigns of John McCain and John Kerry. The Romney campaign renewed this argument on Sunday.
In fact. Sen. Kerry (D-MA) had released 20 years of tax returns when he ran for president in 2004.
Details at the link.