Senator Kamala Harris, a Democrat from California, speaks during a Senate Homeland Security and Governmental Affairs Committee hearing in Washington, D.C., on Thursday, March 7, 2019.

Democratic U.S. Senator Kamala Harris released on Sunday 15 years of tax returns through 2018, offering the most complete look to date at a presidential candidate's finances.

Harris held public office during the years 2004 through 2018. With her husband, Douglas Emhoff, an attorney, she had a combined adjusted gross income in 2018 of about $1.89 million, and paid total taxes of about $697,000, according to the returns.

Harris and Emhoff, who have filed joint tax returns since marrying in 2014, have paid more than $2.2 million in federal taxes over the past five years at an average effective tax rate of 32.6 percent, according to her campaign.

Harris' release of her tax filings follows that of fellow White House contenders like Senators Kirsten Gillibrand and Elizabeth Warren. Senator Bernie Sanders has said he will release his tax filings this week. Tax day is April 15 in the United States.

Democrats in the 2020 race have released their tax returns as Republican President Donald Trump resists moves by congressional investigators to review his tax filings in probes related to his businesses and Russian interference in the 2016 presidential election.

Trump is the first modern U.S. president not to release his tax returns to the public.

After taking control of the House of Representatives in the 2018 elections, Democrats passed a bill that would require presidential candidates to release their tax returns. It has not been voted on by the Senate, which is controlled by Republicans, but Harris supports such legislation.

Harris has also called for the repeal of the Republican tax law approved in 2017 that delivered major tax cuts to the wealthy and businesses.

In 2018, about $157,000 of Harris and Emhoff's $1.89 million in income came from Harris' salary as a U.S. senator, with the bulk of the rest reported as partnership income from Emhoff's work at a law firm.

Before her marriage to Emhoff, most of the income Harris reported each year was from the salary she earned as California's attorney general and, before that, as San Francisco's district attorney.