Rand Paul, the Republican senator from Kentucky, announced on his website Tuesday morning that he's running for president. He says he's "a different kind of Republican leader," by which he means a libertarian kind. The closer he gets to the presidency, however, the less libertarian he gets. His evolution is a case study in how hard it is even for a talented politician to remake his party.

Paul argues that his concern for civil liberties, skepticism about foreign intervention and willingness to back off in the War on Drugs will win him the support of voters who have never pulled the lever for a Republican. He has spoken often about bringing more minorities and young people into the Republican tent. He hopes to rebrand his party the way Bill Clinton did when he ran, in 1992, as a "different kind of Democrat." But while Clinton had some success at remaking his party, so far Paul's party is remaking him.

Paul has shifted most on national-security issues. Last summer, he switched from skepticism to enthusiasm about bombing Islamic State militants. In March, he signed a letter from Republican senators warning Iran's leaders that any nuclear deal they agreed to might not outlast Barack Obama's presidency. Then he sponsored an amendment to boost defense spending, which he had tried to cut in his first year in office.