Both Senators voted in favor of the federalization of elections but Sinema diverged from her colleague and opposed the elimination of the filibuster.
The Arizona Democratic Party censured Kyrsten Sinema for her vote opposing the elimination of the filibuster. When asked during his debate with then Senator Martha McSally whether he would support getting rid of the Senate filibuster, Mark Kelly avoided a straight answer and said instead that he would give it "careful consideration" if such a vote came up. As one could have guessed, and as it turns out, such an answer really means that he would, and did, vote to scrap the filibuster.
The filibuster allows the minority party in the US Senate to block a vote on a bill unless 60 of 100 Senators favor it, rather than a simple majority of 50. The purpose of the measure is to foster deliberation and avoid rash and careless actions by law makers. Currently only budgetary measures - via budget reconciliation - and judicial appointments can pass the Senate on a simple majority vote.
After Arizona Republican and Air Force veteran Martha McSally lost the election for Jeff Flake's former Senate seat to Kyrsten Sinema in 2018, governor Doug Ducey appointed her to late John McCain's Senate seat. McSally proceeded to lose this seat to former astronaut Mark Kelly in the 2020 election. In the same election season Republicans lost two more Senate seats in Georgia. Republicans and Democrats each currently hold 50 Senate seats - this includes two independents that caucus with the Democrats. Vice President Kamala Harris breaks ties with her vote, giving the Democrats - narrow - control over the Senate.