WASHINGTON - Republican presidential candidates Donald Trump, Ted Cruz and Marco Rubio have failed to release their tax returns despite promises to do.

Mitt Romney offered Republican presidential candidates this advice about a hard-won lesson: Release your tax returns before the primaries and avoid tough scrutiny later. But the top three Republicans leading in national polls don't appear to be listening.

Hillary Clinton and Jeb Bush have already disclosed years' worth of their tax returns.

There is no legal requirement to share tax returns with the public, but every major party nominee since 1976 has done so - often well-before winning the nomination.