It’s become a common talking point for “Never Trump” Republicans seeking to defeat President Trump in the 2020 GOP primaries: Polls have found that a substantial number, maybe 40 percent, of Republican voters say they would be open to a primary challenge to the president. Those surveys, the “Never Trumpers” argue, show that Trump is particularly weak and vulnerable to a serious primary challenge.

The problem is that it is common for voters to say they are open to a primary challenge to the president of their own party. It happened to former President Barack Obama in 2010-2011, before Obama went on to win re-election. It also happened to Bill Clinton in 1994-1995, before Clinton went on to win re-election. It did not happen to George W. Bush in 2002-2003, but that was because of strong Republican support for a wartime president.