In a quirk dating back to the origins of Congress, members-elect in the House will cast their vote for the new speaker before taking the oath of office.
The Constitution does not outline how the House should be organized other than to say it should choose its speaker and other officers, determine its rules and publish a journal of its business.
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In the first Congress, Frederick Muhlenberg of Pennsylvania was chosen the speaker on April 1, 1789, the first day a quorum was reached. It was not until days later that the House approved the form of the oath to be taken by members.
One reason is that the office of the speaker was modeled after the British parliamentary system, where it is the parties that choose who lead their caucuses and, if they are in the majority, the government.
On Thursday, after the chaplain offers a prayer, the clerk leads the House in the Pledge of Allegiance and a quorum is confirmed, the two parties will nominate and vote on the next speaker. With the Democrats now in the majority, that will be Rep. Nancy Pelosi of California.
The dean of the House, Rep. John Dingell, D-Mich., will then administer the oath of office to the new speaker, who will in turn administer the oath to members-elect.
The original oath spoke only of supporting the Constitution. But it was revised during the Civil War, when the loyalty of members was under question, to add that representatives would "defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same ...."
The procedure is different in the Senate, where the vice president, who serves as president of the Senate, swears in new members before the election of officers.
• Get complete coverage in FOXNews.com's Senate Center.