Even Republican leaders, such as Mitt Romney, the Republican candidate in 2012 who dithered on releasing his own forms, have called on Trump to release his returns.“I will absolutely give my return, but I’m being audited now for two or three [years’ worth] now so I can’t,” Trump has claimed.

But do voters actually care if Trump doesn’t release his returns?

According to data collected for Fortune by polling firm Morning Consult, the answer is yes for a significant number of people.

Among 1,931 registered voters polled, 45% said that not releasing a tax return made them view Trump less favorably. Furthermore, 37% of likely voters said it made them less likely to vote or him. Those numbers are essentially the same for independent voters, a constituency that Trump needs to win over, and one that an outsider candidacy could in theory do well in.

Then there is the issue of what could actually be in Trump’s tax returns and how that could impact his candidacy.

Trump has claimed to give many millions away in charity, but the Washington Post has found evidence that Trump has given less than $10,000 of his own money to charity since 2008. If the returns showed that Trump had donated less to charities than he has previously claimed, a significant chunk of people—including 45% of Republicans and 41% of independent voters—say that will make them less likely to vote for him.

If the returns showed he paid an effective tax rate lower than the average American, 41% of both registered voters and independents say they are less likely to vote for him. But registered Republicans care much less, with only 19% saying that it would make them less likely to vote for him.

What else could Trump’s tax returns reveal about his business record? Read Shawn Tully’s take.