Reagan wasn't involved in politics, nor held elected office at the time. He became a Republican in 1962, and remained a Republican.
Gabbard was an elected Democrat member of the House from Hawaii, and it wasn't until the year after she'd left office in 2022, that she changed parties. She was still a Democrat, and in office when she actively endorsed and campaigned for commie Bernie Sanders.
Why did she endorse Bernie?
As I said I am not bought into her but open to people changing.
Reagan had to go through a journey to find his clear thinking. Often most people do.