WASHINGTON (Reuters) -A senior Trump administration official who helped lead a regulatory effort seeking to rein in social media companies was sworn in to the five-member Federal Communications Commission (FCC) on Monday. The Senate voted 49-46 last week along party lines to confirm Nathan Simington, who has served at the Commerce Department, to the FCC. U.S. President Donald Trump has railed against social media companies and demanded repeal of a protection known as Section 230 that is part of a 1996 law. FCC Chairman Ajit Pai administered the oath of office to Simington on Monday. Trump has threatened to veto an annual defense bill unless Congress agreed to revoke Section 230. Section 230 protects tech companies from liability over content posted by users. It has been under attack by Trump and Republican lawmakers, who have criticized internet platforms’ content moderation decisions and accused them of stifling conservative voices. Trump in May directed the Commerce Department to file a petition with the FCC seeking to curb legal protections for social media companies. The president tapped Simington after abruptly pulling his nomination of Republican FCC Commissioner Michael O’Rielly for a new term in August. O’Rielly had questioned whether the FCC had authority to issue social media regulations limiting Section 230 protections. Simington said earlier he will get guidance from FCC ethics lawyers before deciding whether to participate in Section 230 proceedings. Pai will step down on Jan. 20, which will result in the FCC being deadlocked 2-2. Some officials think a Republican-led Senate might not confirm a Biden appointee to the commission for months, if not longer. That could stymie Democratic priorities on a number of issues at the FCC, including moving to restore the 2015 net neutrality rules overturned in 2017. Two runoff elections in Georgia on Jan. 5 will determine control of the Senate. Democrats must win both races to wrest control from the Republicans.