Hansi Lo Wang | Michigan Radio
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Hansi Lo Wang

Updated at 7:54 p.m. ET

President Trump says he is looking into delaying the 2020 census, hours after the Supreme Court decided to keep a question about citizenship off the form to be used for the head count.

Trump tweeted that he has asked lawyers whether they can "delay the Census, no matter how long, until the United States Supreme Court is given additional information from which it can make a final and decisive decision on this very critical matter."

Challenges threatening the upcoming 2020 census could put more than 4 million people at risk of being undercounted in next year's national head count, according to new projections by the Urban Institute.

The history of the U.S. census asking about people's citizenship status is complicated.

Many of the stops and starts have been unearthed as part of the legal battle over the decision by Commerce Secretary Wilbur Ross, who oversees the Census Bureau, to add a citizenship question to the 2020 census.

Steven Dillingham, the new director of the U.S. Census Bureau, is refusing to step into the controversy surrounding a potential question for the upcoming national head count.

The hotly contested question asks, "Is this person a citizen of the United States?"