As more presidential candidates release their tax returns, a picture of Democrats’ charitable giving is beginning to emerge. For the most part, they’re not as generous as most Americans.

With notable exceptions, most high-polling 2020 Democratic presidential candidates gave well below the U.S. average to charity in 2018, according to the deductions claimed on their tax returns. While Americans give between 2 percent and 4 percent of their incomes on average, most candidates claimed charitable deductions of less than 2 percent of their total incomes.

Senators Bernie Sanders, Elizabeth Warren and Cory Booker gave more than 2 percent of their total incomes, according to their returns. Beto O’Rourke, the former Texas congressman, gave the least, with donations of just $1,166 in 2017 or 0.31 percent of his income. O’Rourke hasn’t yet released his 2018 return.

Booker, New Jersey’s junior senator, in 2018 claimed the highest charitable deduction at 16 percent, or $24,000. Last year, he relied on his Senate income but in earlier years, Booker, who is single, has made significantly more money in speaking fees and book royalties.

The lack of giving is unlikely to be a big campaign issue, and as President Donald Trump continues to shield his tax returns from release, it’s impossible to know how he compares. However some candidates are already getting sharp questions about the lack of giving, especially in the context of their calls for policies and programs to help the poor.

At a town hall at the University of Virginia last week, a student asked O’Rourke why his donations were so low.

“I do my best to contribute to the success of my community, my state and now of my country. There are ways that I do those that are measurable. There are charities that we’ve donated to that we have recorded and itemized, others we have donated to that we have not,” O’Rourke said.

In a separate conversation with reporters last week, O’Rourke said he and his wife were reaching out to charities to tabulate contributions that don’t show up on his tax returns. An O’Rourke spokesman did not respond to a new request for comment.

A moderator at a Fox News town hall with Sanders last week suggested that the Vermont senator’s giving as a percent of income, 3.4 percent, seemed low. “My wife and I do give money to charity, all right, and we’re proud to do what we did there,” Sanders said.

Sanders spokeswoman Arianna Jones said in a statement to Bloomberg that Sanders’ giving was in line with the rest of the country and that the senator gave to senior centers and environmental and housing advocacy groups, among other nonprofits. She said Sanders believes that “while voluntary charitable donations are commendable, they can never replace ongoing public investments in major social programs and services that improve people’s lives.”

Former Vice President Joe Biden declared his candidacy only on Thursday and has not released his recent tax returns. The returns most recently made public, in 2015, showed that he gave about 1.8 percent of his income to charity, or $6,920.

Americans typically give between 2 percent and 4 percent, according to the Indiana University Lilly Family School of Philanthropy’s Philanthropy Panel Study. Although charity took a beating after the 2008 financial crisis, philanthropy is still a stronger part of the U.S. culture than other developed nations and many Americans see charity as a signal of what issues people care about, according to Una Osili, associate dean for research at the Lilly Family School.

“Giving is something that really does unite Americans. Giving in America is very broad-based and cuts across income, race and ethnicity,” Osili said.

Since entering office, Trump has given his entire presidential salary to various government agencies. It’s impossible to know how much, if anything, he gave to charity because he hasn’t released his tax returns.

According to reports in the Washington Post and other media organizations, Trump has claimed or pledged to give money and not followed through. His charitable foundation was largely funded by others and sometimes spent money to benefit Trump himself.

The New York attorney general sued the Trump Foundation last year, alleging that it used funds for the benefit of the president and his children, and the foundation in December agreed to shut down.

While Vice President Mike Pence hasn’t released his returns lately, which he says he’s done in solidarity with the president, earlier returns showed charitable deductions that outpaced those of most Democratic candidates by a wide margin. In 2015 for example, the vice president claimed charitable deductions of $8,923 on income of $115,526, which comes to a rate of about 7.7 percent. His giving in previous years ranged between 5.4 percent and 9.2 percent.

Booker, who released his tax returns this week, donated by far the most of his income to charity of the major candidates who have released their tax returns. In 2018, the senator gave $24,000, amounting to nearly 16 percent of his total income. In 2013, he gave almost 49 percent of his income to charity, and over the past 10 years, he’s given 10 percent.

Warren in 2018 gave $50,128 on $905,742 for a rate of 5.5 percent, which came in second among the major Democratic candidates.

Senator Kamala Harris reported no charitable contributions from 2011 through 2013, years when she was California’s attorney general. In 2014, she married Douglas Emhoff, a lawyer, and in 2018, the couple gave 1.3 percent of their income to charities.