The latest issue of Bloomberg Businessweek documents the electoral challenges Republican U.S. senators face from members of their own party.

Alabama Republican Senator Richard Shelby, who boasts a score of 99 percent from leading conservative group Heritage Action for America, is a pillar of today’s GOP establishment. First elected to the House of Representatives in 1978 as a Democrat, Shelby moved to the Senate in 1987 and flipped parties after the Republican revolution of 1994. He’s now the chairman of the Senate Banking Committee and one of his party’s top fundraisers.

This year, that profile may work against him. Shelby, 81, is facing a challenge from the right in his primary, which takes place on March 1, alongside the state’s presidential nominating contest. Senate Majority Leader Mitch McConnell finds himself in a quandary as he tries to hold on to the GOP’s four-seat Senate advantage: On the one hand, he can’t afford to alienate moderate, independent voters in swing states like Florida and New Hampshire, where Senate races are likely to be close; on the other, he’s bound to protect incumbent senators from being challenged from the right, a concern that underpins his decision to block confirmation hearings for any Supreme Court nominee until after the general election in November. “Especially in this atmosphere where there’s a lot of anti-establishment feeling out there, anything can catch fire,” says consultant Ron Bonjean, who worked with the National Republican Senatorial Committee for the 2014 midterms. “For many of these Republicans, the election isn’t Election Day. The election is primary day.”

Focusing on Alabama, the article says nothing about Richard Burr‘s re-election bid in North Carolina against opposition from Republicans such as Tea Party favorite Greg Brannon.