cross the aisle

(chiefly US, idiomatic, politics) To vote, unite, or otherwise co-operate with members of another political party in order to achieve governmental or political action.

(chiefly Britain and Canada, idiomatic, politics) Of a member of a parliament, to resign from one's political party and join another party, resulting in moving from one's currently assigned desk or seat in the legislative chamber to a new desk or seat physically located with the other members of one's new party.