JEFFERSON CITY, Mo. — Josh Hawley, the Republican running for Senate in Missouri, said Wednesday it's possible that President Trump would be able to end birthright citizenship for illegal immigrants through an executive order, but said he'd need more time to study Trump's plan.

Hawley, Missouri's attorney general and a constitutional lawyer, said in a call with reporters that he's also worried about "chain migration," or family-based migration. He said Trump's push for an executive order to end birthright citizenship appeared to be aiming at changing the naturalization process, not the Constitution as some feared.

That can "certainly" be done by statute and "maybe" by executive order, Hawley said. Nevertheless, Hawley predicted the president's plan would be considered by courts "sooner or later."

Trump's plan hinges on the 14th Amendment, which grants citizenship to “all persons born or naturalized in the United States," but says they must be "subject to the jurisdiction" of the United States. Conservatives note the Supreme Court has never ruled on whether that clause can be used to exclude illegal immigrants, while opponents of the plan say Trump's order would violate the Constitution.

[More: Paul Ryan breaks with Trump: 'You cannot end birthright citizenship with an executive order']

Hawley is campaigning for the Senate against Democratic incumbent, Sen. Claire McCaskill. The pair are fighting it out in one of the tightest races in the country, and the national debate on immigration has served as an energizing issue for the GOP base in Missouri despite it not being a border state.

McCaskill told the Kansas City Star on Tuesday and the Associated Press on Wednesday that she does not believe “any president can change the Constitution through executive order,” but did not comment on whether babies born in the U.S. to noncitizens should be extended automatic citizenship.

Hawley has continually hit McCaskill for her votes on border security measures and a bill that granted illegal immigrants with a pathway to citizenship. The National Border Patrol Council in September endorsed McCaskill. The incumbent called Trump's southern border wall rhetoric "embarrassing" during a 2017 Senate Homeland Security Committee meeting, according to Politifact.