Washington ? With control of the health care debate slipping from his grasp, President Barack Obama pitched his ambitious plan to both conservative talk radio and his own liberal supporters Thursday — and denied a challenge from one backer that he was “bucklin’ a little bit” under Republican criticism.

Liberals were on the verge of revolt as Obama refused to say any final deal must include a government-run insurance option, while Republicans pressed their all-but-unified opposition to the White House effort. Obama, who will leave Washington today on vacation, said reason would prevail and it was no time to panic.