The incumbent senator offers his party more than his rival. On Tuesday, Republican primary voters will place their bets in a gamble of national importance to their party. The Democrats now hold a one-vote majority in the U.S. Senate. One man, either veteran Senator Bob Smith or three-term Rep. John Sununu, will emerge next week to face Democrat Jeanne Shaheen. The other will have to leave Congress. Of the two, Smith offers his party its best hope of retaining the seat. Not incidentally, Smith would also make the better senator. The candidates differ little in philosophy. Both have strong conservative...