The longer Donald Trump waits to release his tax returns, the greater the suspicion that he has something to hide.

Rep. Anna Eshoo believes voters have the right to expect presidential nominees to be transparent about their finances. The California Democrat on Tuesday introduced legislation requiring candidates to publicly disclose their three most recent personal income tax returns. Similar legislation was introduced in the Senate by Sen. Ron Wyden D-Oregon.

The only question is whether three years is enough to provide a good picture of financial history. Five or 10 years would be better.

For more than three decades, presidential nominees from both parties have released at least five years’ worth of tax returns-with two exceptions: Republicans John McCain in 2008 and Mitt Romney in 2012. And even they disclosed two years. Hillary Clinton has released records dating back to 1992.

Republican Senate Majority Leader Mitch McConnell said last week that Trump should release his returns. But don’t expect McConnell or Speaker of the House Paul Ryan to let Eshoo’s legislation come up for a vote.

Eshoo’s bill would require candidates to release three years of tax returns within 30 days of being nominated by their party. If they don’t, the Secretary of the Treasury would be required to provide copies of the returns to the Federal Election Commission for public disclosure.

Romney was hounded with demands to disclose his tax returns to illuminate the details of his fortune. When voters learned he paid only 14 percent taxes on his 2010 return — far less than the 30 percent that the top 1 percent of earners generally pay — the uproar damaged his standing and helped Barack Obama’s campaign to paint Romney as out of touch.

Trump knows this. So he alternates between saying his finances “are none of your business” and telling reporters he’ll release them after the IRS completes an audit.

If the GOP lets him get away with hiding his returns, it will set a dangerous precedent.

With Trump it’s especially important: This is a candidate who uses his bully pulpit (and we do mean bully) to malign a highly respected judge hearing against one of his businesses. Who knows how he’d use the power of the presidency to advance his financial interests?

Voters need to know what those interests are.