RICHMOND, Va. — Dave Brat, a local economics professor, toppled House Majority Leader Eric Cantor on Tuesday night in the most shocking primary defeat since Republicans took the House in 2010. The conservative challenger’s victory halts one of the most meteoric rises in national politics, and illustrates the strong anti-incumbent fever that has taken over Cantor’s Richmond-area district. Cantor is the second House incumbent to lose this primary season — Texas GOP incumbent Ralph Hall was defeated by a tea-party backed challenger at the end of May. Cantor’s defeat not only reorders Virginia politics, where Cantor was the highest-ranking Republican,...