Wiktionary
vb. (present participle of cross the floor English)
Wikipedia
In politics, crossing the floor is when a politician changes their allegiance or votes against their party in a Westminster system parliament. Crossing the floor may be voting against the approved party lines, or changing to a second party after being elected to a first party. While these practices are legally permissible, crossing the floor can lead to controversy and media attention. As well, voting against party lines may lead to consequences such as losing a position (e.g., as minister or a portfolio critic) or being ejected from the party caucus.
The term originates from the British House of Commons, which is configured with the Government and Opposition facing each other on rows of benches. An MP who switched parties would literally need to cross the floor. A notable example of the latter is Winston Churchill, who crossed the floor from the Conservatives to the Liberals in 1904, before later crossing back in 1924.
Usage examples of "crossing the floor".
Bili against the wall, some men crossing the floor, the girl singing on the table, all the laughing men sitting around her.
He grabbed up his robe from the foot of the bed and pulled it on over his trembling, naked body, and began crossing the floor to the door.
Springing quickly to his feet he blew out the lamp, and crossing the floor silently locked the door.