Democrats are ramping up their attacks on Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE for refusing to release his tax returns.

Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE's campaign, Democratic lawmakers and liberal activists are all trying to make the case that Trump’s refusal shows he has something to hide.

Clinton, who has made more than 30 years of her returns public, has even suggested Trump's returns may show that he pays no taxes.

ADVERTISEMENT

“If you've got someone running for president who's afraid to release his tax returns, because it will expose the fact that he pays no federal income tax, I think that's a big problem," she said on NBC's “Meet the Press” earlier this month.

The Washington Post reported that in 1978 and 1979, Trump claimed negative income and as a result did not pay any federal income tax.

The Clinton campaign also released a video earlier this month that directly asks "What's Donald Trump hiding?"

Trump has repeatedly said that he will release his tax returns after the Internal Revenue Service (IRS) is done auditing him. A spokeswoman for Trump reiterated that point to The Hill on Friday.

The IRS, however, has said that there is nothing that stops taxpayers from releasing their own information.

Trump adviser Paul Manafort recently told the Huffington Post that “the only people who want the tax returns are the people who want to defeat him.”

But Democrats are pointing to polls showing that most voters want Trump to release his returns. They say that Trump would be the first major-party nominee in about 40 years not to release his returns.

The returns are just one of several financial issues the left is raising against Trump, who has touted his experience as a businessman on the trail.

Democrats have also hammered Trump in recent weeks for a tax plan that economists say disproportionately benefits the wealthy and for comments he made in 2006 saying he hoped that the real-estate market would tank.

"I sort of hope that happens because then people like me would go in and buy," Trump had said.

Sen. Elizabeth Warren Elizabeth WarrenBiden's fiscal program: What is the likely market impact? Warren, Schumer introduce plan for next president to cancel ,000 in student debt The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon MORE (D-Mass.), a liberal giant who is often floated as a possible running mate for Clinton, blasted Trump on his tax returns Tuesday at the Center for Popular Democracy’s annual gala.

“I mean look, maybe he is just a lousy businessman and he doesn’t want everyone to know that he’s not as rich as he claims to be,” she said. “But we do know this, the last time that his taxes were made public, Donald Trump paid nothing. Zero. Zero. Zero taxes before, and for all we know, he’s paying zero taxes today.”

Warren also hammered Trump for saying that he works to pay as little in taxes as possible because the country throws money down the drain.

“Programmers and engineers and small business owners, they pay their fair share to support our military who show courage and sacrifice every day,” Warren said. “Donald Trump thinks that supporting them is throwing money down the drain. Then I say we throw Donald Trump down the drain.”

Sen. Ron Wyden Ronald (Ron) Lee WydenGOP senator blocks Schumer resolution aimed at Biden probe as tensions run high Republican Senators raise concerns over Oracle-TikTok deal Hillicon Valley: TikTok, Oracle seek Trump's approval as clock winds down | Hackers arrested for allegedly defacing U.S. websites after death of Iranian general | 400K people register to vote on Snapchat MORE (D-Ore.) has also introduced a bill that would require presidential nominees to release their tax returns. Warren and Democratic Sens. Michael Bennet Michael Farrand BennetOVERNIGHT ENERGY: House Democrats tee up vote on climate-focused energy bill next week | EPA reappoints controversial leader to air quality advisory committee | Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' Senate Democrats demand White House fire controversial head of public lands agency Next crisis, keep people working and give them raises MORE (Colo.) and Barbara Boxer Barbara Levy BoxerThe Hill's Morning Report - Presented by Facebook - Biden, Harris launch Trump offensive in first joint appearance Bottom line Polls show big bounce to Biden ahead of Super Tuesday MORE (Calif.) are co-sponsors.

Wyden, the top Democrat on the Senate Finance Committee, stressed that his bill would apply to all nominees, but the reasons he gave for the bill mirror the attacks on Trump.

“Tax returns give honest answers” such as what rate someone pays of if they even pay taxes at all, Wyden said.

Progressive groups have also been making a push for Trump to release his returns.

A petition on the matter sponsored by groups including the AFL-CIO, Americans for Tax Fairness Action Fund, CREDO Action and Democracy for America had more than 75,000 signers as of Friday afternoon. A separate petition from CREDO had more than 54,000 signers.

CREDO Vice President and Political Director Murshed Zaheed said Trump’s financial disclosure report showed that he has investments in companies that he's criticized on the campaign trail.

Trump’s tax returns “are sure to reveal even more,” he said.

ATF Action Fund and other groups also held an event in front of a hotel Trump is developing near the White House to make their case.

“We want to know what he’s trying to hide,” ATF Action Fund Executive Director Frank Clemente said.

Trump's resistance to releasing his tax returns has divided Republicans.

Some, including Republican National Committee Chairman Reince Priebus, have stood by the candidate. Priebus told “Fox and Friends” earlier this month that he’s not sure voters really care about Trump releasing his returns.

But others, including 2012 GOP nominee Mitt Romney and former IRS Commissioner Mark Everson, have called on Trump to release them.

Democrats see a potent issue and plan to hammer away at Trump in the months to come.

Democratic strategist Holly Shulman said that Trump’s tax returns will be a big issue for him because he has made his business experience central to his campaign.

“If you’re going to try to run on your record of business, then you need to show us what you’ve done,” she said.

“They’d be crazy not to,” said Democratic strategist Brad Bannon, about keeping up the pressure on Trump.

Bannon added that he believes the issue will stick in voters' minds.

“This tax thing with Trump could turn out to be his version of Hillary Clinton’s email,” he said.