Alexander's Win Keeps Senate Incumbents' Record Perfect - Twenty Senators From Both Parties Have Won in Primaries So Far This Year, None Have Lost

From The Wall Street Journal:

WASHINGTON—With most of the year's competitive Senate primaries now over, here's one way to score it so far: Incumbents, 20; Challengers, 0.

The results have underscored the strong advantages and durability that incumbents carry into elections. The latest example came Thursday, as Sen. Lamar Alexander of Tennessee overcame several challengers to win his Republican primary election.

His win, combined with that of Sen. Pat Roberts (R., Kan.) earlier this week, means no Senate Republican incumbent will lose a fight for renomination this year, a first since 2008.