Gov. Chris Christie of New Jersey ramped up his tough talk on foreign policy on Monday, calling President Obama a “weakling” and saying that the United States should threaten to shoot down Russian planes conducting airstrikes in Syria. “My first phone call would be to Vladimir, and I’d say, ‘Listen, we’re enforcing this no-fly zone,'” Mr. Christie said on MSNBC. “And I mean we’re enforcing it against anyone, including you. So don’t try me. Don’t try me. Because I’ll do it.” Christie went on to say that Mr. Putin was “punching above his weight” and called Mr. Obama “this weakling in the White House.”