President Trump may be excluded from the nation's largest primary election after California Gov. Gavin Newsom signed a bill into law on Tuesday that would require presidential hopefuls to release their tax returns in order to appear on the ballot.

The law — known as the Presidential Tax Transparency and Accountability Act — mandates that all presidential and gubernatorial candidates must disclose five years of income tax returns at least 98 days before a primary election.

"As one of the largest economies in the world and home to one in nine Americans eligible to vote, California has a special responsibility to require this information," Newsom said in a statement. "These are extraordinary times and states have a legal and moral duty to do everything in their power to ensure leaders seeking the highest offices meet minimal standards, and to restore public confidence."

California's new bill was approved overwhelmingly by the state legislature early this month and is a direct challenge to Trump, who in 2016 broke the long-standing norm of presidential candidates releasing their tax returns. Trump first claimed he was under audit and later alleged that his taxes were not of concern to the American people.

The White House has also bucked several attempts from congressional Democrats and activists to obtain the president's taxes and examine business deals for possible fraud.

"This bill was necessary because President Donald Trump has departed from over four decades of established political tradition, respected by both Democrats and Republicans alike, by refusing to release his income tax returns," Frank Clemente, the executive director of Americans for Tax Fairness, said in a statement. "Clearly, there is something in those tax returns he doesn't want the public to see."

The Republican National Committee (RNC), however, ardently rejected the law, saying in a statement to Cheddar that the state is attempting to deny voting rights to millions of Californians.

RNC Chairwoman Ronna McDaniel also said on Twitter that California Democrats are "resorting to gimmicky tactics that are unconstitutional, undemocratic, and just plain dumb."

California's legislation comes just weeks after New York passed its own law requiring state officials to disclose the tax returns of Trump and other elected officials upon request from Congressional committees.

"No one should be allowed to run for the highest office in the land while burying the truth from voters," Ryan Thomas, a spokesperson for the progressive advocacy group Stand Up America, told Cheddar in response to California's law. "The American people deserve transparency about Trump's massive conflicts of interest and foreign entanglements."

Newsom also added that the tax disclosure required by his state's law would expose "conflicts of interest, self-dealing, or influence from domestic and foreign business interest."

However, the mandate has been criticized as a possible privacy violation. Nate Silver, the editor in chief of FiveThirtyEight, said on Twitter that the law is a "terrible, anti-democratic idea and California should be embarassed [sic]."

The law is expected to be challenged in the courts, which could delay its enforcement until after the 2020 election.

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