None; they are required to provide a financial disclosure form, sign it, and submitted to the elections commission. There are absolutely no requirements for financial records, tax returns, or other documents. It has been the recent pattern to release two years of tax returns; Mitt Romney has released one year, and will release the second year when the taxes are complete (he's on an extension at the current time until his tax records can be compiled). In 2008, both Barack Obama and John McCain released two years of tax records, and there was no discussion at that time for additional years of disclosure. in 2008, when John McCain considered Romney as a potential running mate, he requested 20+ years of tax returns, and Mitt supplied them. John McCain said there was nothing in them which would exclude Romney from consideration.