The Trump administration’s plan to include a citizenship question on the 2020 census encountered some skepticism Tuesday from the U.S. Supreme Court as the justices probed the reasons why the U.S. Commerce Department added the question and its potential impact on the census’s accuracy.

After an extended argument, however, it appeared the Supreme Court could divide along ideological lines on what is the most significant Trump policy fight to come before them since they ruled 5-4 last term to uphold the administration’s immigration travel ban.