Conservative Republicans on Wednesday insisted the party was better off without Arlen Specter, the Pennsylvania senator who defected to the Democrats, even as moderate Republicans warned that the party risked marginalising itself into irrelevance.

Pat Toomey, the right-wing Republican whose challenge for the Pennsylvania Senate seat prompted Mr Specter’s defection, said his rival had “always been a fish out of water” in the Republican party and had finally found his “ideological home” on the left.