US Presidents Trivia: What President was not allowed to attend his party's national convention by the Secret Service?

One of the highlights of virtually every Presidential nominating convention is speeches by the incumbent President or former President's.  With relatively few exceptions (2008 being one of them), former/current President's are welcomed with open arms and seen as rallying points for their party.  However, this isn't always the case - in some cases, President's are unpopular and seen as relics of the past.  And in at least one case, the Secret Service refused to allow a President to attend his party's nominating convention due to fears on his life.  So, off of Pocket Trivia: US Presidents - What President was not allowed to attend his party's national convention by the Secret Service?  Was it Abraham Lincoln, John Kennedy, Lyndon Johnson or Woodrow Wilson?

The correct answer to this one would be Lyndon Johnson and the fun-filled 1968 Democratic National Convention.  As you can see from the above pic, it was a rockin good time.

Johnson did not seek renomination from the Democratic party as a result of ill health and tanking popularity (caused by the Vietnam War).  Fearing for his safety, the Secret Service didn't allow (well, told him not to would probably be a better way of describing it) Johnson to attend the convention, fearing that his appearance would cause riots.

Of course, that was a silly worry - riots happened anyway!  The lasting implication of the 1968 DNC was the antiwar riots that plagued Chicago during the convention.  10,000 protested and faced off against 23,000 national guardsmen and police.

Good thing Johnson didn't show up!