From Fortune:

With impeachment on the horizon, Kristen Nyman, a government affairs specialist at R Street Institute and a former legislative assistant for Rep. Rod Blum, believes Republicans will “begin to distance themselves from the President on issues that won’t impact their own re-election.”

In fact, Nyman points to the fact that many conservative voters support a strong national defense.

Nyman notes that support for Trump has diminished slightly in Graham’s home state of South Carolina, so he may be “taking this low-risk opportunity” to distance himself from the president, while reasserting his own strong position on defense.