Wiktionary
cross the aisle
vb. 1 (context chiefly US idiomatic politics English) To vote, unite, or otherwise co-operate with members of another political party in order to achieve governmental or political action. 2 (context chiefly British and Canada idiomatic politics English) 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.