Mary Matalin, a high-profile political pundit and veteran strategist for the Republican Party, changed her party registration to Libertarian from Republican, she said on Thursday. But in an interview with Bloomberg, which reported on the switch, she emphasized that her decision was not connected to Donald J. Trump’s being the presumptive Republican presidential nominee. She described herself as a voter as a “provisional Trump” and a “never Hillary,” referring to the leading Democratic candidate, Hillary Clinton. Pressed on Thursday about why she switched political parties, Ms. Matalin told Bloomberg Politics that she was a Republican in the “Jeffersonian, Madisonian sense.”...