Back in the day, when there were liberal Republicans — Javits, Lindsay, Hatfield — Charles McC. Mathias was a liberal Republican Congressman and then Senator from Maryland. As befits someone whose great-grandfather ran downballot from Lincoln, Mathias was a loyal Republican; he went so far as to endorse Barry Goldwater for President. He has known John McCain since before McCain first held public office.
Mac Mathias endorsed Barack Obama today.