WASHINGTON — As the most gifted orator of his generation, President Obama finds speechmaking perhaps his most potent political tool. It propelled him to national prominence in 2004 and to the White House in 2008. And whenever he needs to calm economic fears or revive stalled health care legislation, he takes to the lectern.

But the limits of rhetoric were on display last week when the president could not rescue two foundering candidates in governor’s races in New Jersey and Virginia. Has Mr. Obama lost his oratorical touch? Is the magic finally beginning to fade? Does the White House rely too heavily on his skills on the stump to advance his priorities?

It may be too soon to reach such conclusions. The Democrats who lost last week, after...