Sen. John Kerry, the Democrats’ 2004 presidential nominee, said Mitt Romney, the current Republican presidential nominee, and his running mate, Rep. Paul Ryan, would be the “most inexperienced foreign policy twosome” to run for the White House in decades.

In an energetic and humorous speech of a kind that he rarely delivered when running for president himself, an animated Mr. Kerry jabbed at Mr. Romney as he ticked off the successes of President Barack Obama’s foreign policy.

In one of his most effective passages, Mr. Kerry, the senior senator from Massachusetts, mocked his own misstep in 2004 when he said said he was for funding the Iraq war before he was against it…