The deciding source is the United States Congress, through the Congress.gov member lists and the Congressional Record. A party controls the Senate if its own members hold at least 51 seats, and the House if they hold at least 218 seats, on January 3 of the year after the 2028 election. Only a party's own members count, so independents are not counted toward any party, even if they caucus with one. If the Senate is split 50 to 50, the majority goes to the party of the Vice President, who casts tie-breaking votes: the party of the president-elect in a presidential election year, and otherwise the party that holds the Presidency. In presidential election years, the presidency goes to the party of the president-elect named in the Declaration of the Election of President and Vice President in the Congressional Record, with party affiliation taken from public information because the record does not state it. The outcome matching the resulting combination of party control is Yes and all others are No. Resolution is at 9:00 AM CT on January 7 of the year after the election, or earlier if the Associated Press, The New York Times, and The Wall Street Journal have called all House and Senate races and, in a presidential election year, the presidential race for the same candidate, with no ongoing or announced recount, legal challenge, or other official proceeding that could reasonably affect the result. If the Congressional Record is delayed, resolution waits until it is published.

The deciding source is the United States Congress, through the Congress.gov member lists and the Congressional Record. A party controls the Senate if its own members hold at least 51 seats, and the House if they hold at least 218 seats, on January 3 of the year after the 2028 election. Only a party's own members count, so independents are not counted toward any party, even if they caucus with one. If the Senate is split 50 to 50, the majority goes to the party of the Vice President, who casts tie-breaking votes: the party of the president-elect in a presidential election year, and otherwise the party that holds the Presidency. In presidential election years, the presidency goes to the party of the president-elect named in the Declaration of the Election of President and Vice President in the Congressional Record, with party affiliation taken from public information because the record does not state it. The outcome matching the resulting combination of party control is Yes and all others are No. Resolution is at 9:00 AM CT on January 7 of the year after the election, or earlier if the Associated Press, The New York Times, and The Wall Street Journal have called all House and Senate races and, in a presidential election year, the presidential race for the same candidate, with no ongoing or announced recount, legal challenge, or other official proceeding that could reasonably affect the result. If the Congressional Record is delayed, resolution waits until it is published.