WASHINGTON — Republicans mounted a combative, coordinated drive Monday to salvage Brett Kavanaugh’s Supreme Court nomination as they fought to keep a second woman’s allegation of long-ago sexual misconduct from derailing his confirmation. President Donald Trump leapt to his defense, the Senate’s top Republican accused Democrats of a “smear campaign” and an emotional Kavanaugh declared, “I’m not going anywhere.” In the run-up to an appearance by Kavanaugh and his main accuser at a dramatic Senate hearing, the Republicans embraced their newly aggressive stance with his nomination dangling precariously.