Donald Trump’s cultural and long-term political legacy will be debated for decades. But his legacy for the Republican Party will be tested far sooner than that. He has the power to leave the GOP and the conservative movement intact or disastrously divided. It will all depend on whether Trump runs for president in 2024. For the good of the country, his party, and himself, he shouldn’t. It’s true and recognized by people with open minds that Trump catalyzed some overdue policy shifts in Washington while making inroads with crucial voter blocs. But his deficiencies as a candidate and as a leader compromised and in some cases wasted those gains. The only way for the Republican Party to secure and build on those gains is to move on from Trump himself. Although the GOP lost control...