WASHINGTON—House Republicans backed Kevin McCarthy as speaker in a closed-door meeting Tuesday, a key step he needs toward winning the gavel, with the result also showing that he has more work to do to win the vote of the full chamber on the floor next year. The vote showed the challenge that Mr. McCarthy faces in January when he must win 218 votes in a roll-call vote among all lawmakers present and voting, with a Republican majority that is expected to be the narrowest in recent history. All Democrats are expected to oppose him. Read her reasoning before you criticize:...