If Sen. Rand Paul runs for president and loses, no one will be saving his Senate seat for him. Under Kentucky law, a candidate cannot appear on the ballot more than once, meaning that Paul can't seek reelection for his current job and run for president on the 2016 ballot. Paul's campaign has argued that he's only said he's running for the senate, but he did try to get the law changed.
As The Washington Examiner noted, Kentucky law only allows candidates to appear twice on a ballot under special circumstances that don't apply to Paul. Worse, the deadline to file for the senate race in Kentucky is before the first primary in Iowa. And while the Paul spokeswoman emphasized Wednesday that "the only position Senator Paul has said he is running for is re-election to the Senate," it doesn't seem that way. Throughout the summer Paul has been visiting Iowa, a necessity for possible presidential candidates, and repeatedly attacking his (as of now) likely Democratic opponent, Hillary Clinton.
The argument against a possible 2016 run is even less convincing when you consider that Paul has been worried about this ballot law for several months. In March, The Washington Times reported that Paul lobbied state officials to change the law, on the grounds that it was "unconstitutional." “The purpose of the bill will be to make clear that Rand Paul or anyone in a similar situation in Kentucky can run for both offices in the same year,” Kentucky Senate Majority Leader Damon Thayer told The Times.