Answer: Candidates still matter to some extent!
It's not exactly breaking news that Trump has a strong hold over the GOP. But if you look at the three cases where his endorsees lost tonight, each pick had potential challenges, either because of their own weaknesses as candidates or strong candidates running against them. In South Carolina's 3rd District, Mark Burns had a controversial past that invited outside spending to help his opponent, and Burns also barely raised any money from donors, mostly self-funding his bid with loans. In Colorado's 5th District, Dave Williams had rubbed a lot of people the wrong way as state party chair, to the extent that outside groups spent more than $2.6 million against him or on behalf of his main primary opponent. And Trump doesn't have as firm a hold over GOP politics in Utah, indicative of how his endorsee, Trent Staggs, couldn't beat out the establishment choice in Rep. John Curtis, who had a stronger track record as an incumbent congressman and received a ton of outside support.
—Geoffrey Skelley, 538