Kennedy (D) holds the title of being the President who has issued more PEB's in history, which is even more impressive if you consider that he didn't serve out both terms.
Since 1960, Democrats have used the PEB (61 times) more than Republicans (41 times), which is ironic considering how few Democrats have held the presidency and how much labor supports the Democratic party.
Bush II = 4 (2 being UA/IAM and NW/AMFA)
Clinton = 12 (1 being AA/APA)
Bush I = 4
Reagan = 18 (13 of them dealing with either the LIRR or PATH)
Carter = 10
Ford = 5
Nixon = 10
Johnson = 9
Kennedy = 30
Before that, there hadn't been any hint of presidential intervention with negotiations or strikes at airline unions since 1966, even during the darkest days at Continental or Eastern.
So, before you start making this a party vs. party issue, at least look at the entire picture and realize that in many ways, the Demoncrats have been talking out of both sides of their mouth when it comes to being Labor's Friend.