How unusual is it to cross the aisle for the State of the Union?

The familiar scene of the president addressing a joint session of Congress may look a bit different this year after a proposal that lawmakers take seats irrespective of political affiliation. Usually, Democrats and Republicans sit on opposite sides of the aisle in the House chamber. Several dozen lawmakers have signed on, but just how many take part won’t be known until Tuesday night. It raises a host of questions:

How is seating usually determined in the House?

According to the Congressional Research Service, members of Congress initially drew lots to determine seating in the House.

With the start of the 29th Congress in 1845, seating was determined on a first-come, first-choice basis, and with it began the tradition of members of one party sitting together as a bloc. Then, members of the Whig Party sat to the speaker’s left, and Democrats to the right.

By 1914, individual seats were replaced by long benches. Members occupied any vacant space on their side of the aisle. There is permanent seating for 446 people on the floor.

How is seating determined for the State of the Union?

Presidents George Washington and John Adams delivered their State of the Union addresses — then called the Annual Message — in person. But Thomas Jefferson began a tradition of submitting only written messages that lasted until Woodrow Wilson chose to again make a speech in 1913. It has been delivered in person with only six exceptions since 1934.

For members of the House, except for those in leadership positions, seating today is on a first-come, first-choice basis, with lawmakers traditionally sitting with colleagues from their own party. A member can arrive at any point on the day of the speech to claim a seat, but must remain there in order to hold it.

An area in the chamber is reserved for members of the Senate, who will cross the Capitol as the time of the president’s speech nears.

Additional seats in the well of the House, directly in front of the rostrum, are reserved for the president’s Cabinet, justices of the Supreme Court, the Joint Chiefs of Staff, former members of Congress and members of the diplomatic corps.

Temporary seating is added to accommodate senators and other visiting officials.

Are members required to attend the State of the Union?

Attendance at the State of the Union is not required, and some members routinely skip the president’s speech. In addition, since the Sept. 11, 2001, terrorist attacks, each party’s leadership has selected two members of each chamber to be absent from the Capitol.

What is different this year?

Members of Congress sitting together in party blocs is only a tradition; in fact, members are free to sit wherever they choose.

In response to the Tucson shooting rampage and the almost immediate calls for greater civility in political discourse, some suggested members of Congress break tradition to sit with members of the opposite party.

One of the first to propose the idea was the centrist Democratic group Third Way. Sen. Mark Udall of Colorado quickly agreed, and now dozens of members have announced they will sit with a member of the opposite party, many choosing a colleague from their own state.

Can members of the public attend the State of the Union?

Seating in the House gallery is restricted to ticket-holders. Members of Congress each are allowed to invite one guest; congressional leadership and the White House are given multiple tickets. President Reagan began the tradition of inviting guests to join the first lady. Additional seating behind the speaker’s rostrum is reserved for members of the media.

How long has the address been broadcast?

The first State of the Union to be broadcast to the public on radio was Calvin Coolidge’s in 1923. Harry Truman delivered the first televised State of the Union in 1947.

michael.memoli@latimes.com