Although the White House has said the 2020 census will inquire about residents' citizenship status, President Trump's nominee to oversee the Census Bureau on Wednesday avoided senators' questions on the matter.

The issue has ignited months of debate, as Democrats claim a citizenship question would scare illegal immigrants and lead many to avoid participating in the census. Because the number of congressional seats awarded to each district in the House of Representatives is currently determined by population totals provided by census results -- citizens and noncitizens -- Democrats fear the Trump administration's change will dramatically cut into their representation in Congress.

If confirmed, Steven Dillingham will oversee the once-a-decade census that determines only congressional apportionment, but also how hundreds of billions of dollars in tax revenue are distributed. Dillingham appeared before a Senate panel Wednesday.

Sen. Steve Daines, R-Mont., tried to get Dillingham to weigh in, saying that citizens in “Montana should have more of a say in Washington, D.C., than illegal immigrants harboring in sanctuary cities across the country." But the nominee responded: “I have no plans to voice an opinion on that question.”

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"It makes no sense why a state like California that harbors millions of illegal immigrants is rewarded with additional representation in Congress and taxpayer resources at the expense of more rural states like Montana," Daines told Fox News. "That is rewarding illegal behavior."

Daines added, "It is common sense for a sovereign nation to know how many citizens and noncitizens are in the country."

Several advocacy groups and states, including New York and California, have filed lawsuits seeking to have the citizenship question removed.

Those challenges, legal experts tell Fox News, face an uphill battle because it has traditionally been considered the White House's prerogative to decided whether to inquire about citizenship on the census. Former President Barack Obama's administration eliminated the question in 2010.

"There is no credible argument to be made that asking about citizenship subverts the Constitution and federal law," Chapman University law professor and constitutional law expert John Eastman told Fox News. "The recent move is simply to restore what had long been the case."

California Attorney General Xavier Becerra, in a statement earlier this year, said the issue was critical in his state. California, heavily liberal, is estimated to have far more illegal immigrants than any other state.

“California simply has too much to lose to allow the Trump administration to botch this important decennial obligation," Becerra said. "What the Trump Administration is requesting is not just alarming, it is an unconstitutional attempt to disrupt an accurate census count.”

The tension comes amid another major lawsuit by Alabama, which is suing the federal government to flatly prevent illegal immigrants from counting at all for purposes of reapportioning congressional districts.

Alabama Attorney General Steve Marshall argued that predicted 2020 census numbers will cause Alabama to lose a congressional seat, and thus an electoral vote, to a state with a “larger illegal alien population.”

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That broader lawsuit, which aims to entirely exclude illegal immigrants from the census, could well succeed, Eastman told Fox News.

"I do not believe it would be illegal or unconstitutional for Congress to only count citizens," he said. "Indeed, I have argued in a brief filed in the Supreme Court that the 'excluding Indians not taxed' language in the [Constitution's] apportionment clause requires that only citizens be counted. ('Indians not taxed' was the example at the time of those who were not part of the body politic.)"

Dillingham noted that the courts will determine whether the citizenship question is used and said he’ll have to administer the census consistent with that decision.

"There is no credible argument ... that asking about citizenship subverts the Constitution and federal law."
— Chapman University law professor John Eastman

“It would be problematic, I think, to take a public position on that question,” he said. Earlier in the hearing, Dillingham said the Census Bureau has looked at the use of the citizenship question, “and they have identified the possibility that there could be changes in the responses.” He said the Census Bureau is planning followup work to get people to participate.

The Trump administration announced in March it would include a citizenship question on the 2020 count, saying the Justice Department requested its inclusion to help with enforcement of voting rights laws. But documents released through a lawsuit show Commerce Secretary Wilbur Ross sought to include the question months earlier.

Democrats on the Senate Homeland Security and Governmental Affairs Committee said they wanted the panel to review how the decision evolved and whether Ross was truthful with lawmakers in stating that the Justice Department was responsible.

“It appears to me that a political decision was made to include the question, and then they sought Justice to ask for it so they could hang their hat on that peg. That’s not being honest with us or the American people and it certainly demands oversight,” said Sen. Claire McCaskill, D.-Mo.

Fox News' Steve Kurtz and The Associated Press contributed to this report.