The Senate headed closer to a major showdown over President Barack Obama’s picks for the U.S. Court of Appeals for the D.C. Circuit on Thursday following a party-line vote approving Washington lawyer Patricia Millett’s nomination.

Republicans for weeks have voiced opposition to filling any more vacancies on the D.C. Circuit, often considered the country’s most important court second to the U.S. Supreme Court. The Senate Judiciary Committee vote on Millett’s nomination was the first test of how strongly Republicans would oppose Obama’s nominees.