“This year only 10 percent of the seats in the Legislature are being contested,” says Julia Sass Rubin, an associate professor at Rutgers. “This is a toxic system, and it limits who will run.”
And who will win. No state legislator has lost a primary since 2009. No Congressional incumbent has lost one in half a century.
You can measure the effect in Congressional races, because the districts cross county lines. Amy Kennedy, a candidate for Congress in South Jersey last year, won 75 percent of the primary vote in counties where she had the party line, but just 50 percent in counties where the line went to her opponent, Brigid Harrison, a professor at Montclair State University. So the line gave her 25 percent, a big enough boost to win almost every time.