It seems to be just another political euphemism, in line with politicians not being terribly willing to admit when they are wrong, but is there anything more than that to their use of "suspend" when they exit a primary race? Has there been any primaries candidate that has "unsuspended", i.e. resumed the race after previously announcing a suspension?
There are a couple of reasons why candidates do this. Firstly, because the Federal Election Commission only considers a campaign as "closed down" for good after a winding down process is complete; including the sale of campaign assets and the handling of debts. Not shutting down the campaign for good also allows campaigns to continue accepting money from donors to fund this winding down process and to help pay off debts.
Additionally, suspending a campaign allows it to be "unsuspended"; notably in September 2008, John McCain suspended his campaign for two days in order to focus on the financial crisis. He continued to accept donations throughout this suspension, and resumed it in order to participate in a debate.
Going back another few years, Ross Perot suspended his campaign for three months in 1992, resuming it ostensibly due to motivation from grass-roots supporters. The same article also details the dramatic suspension of Adlai Stevenson's campaign in 1952, a week before election day, in order to respond to a prison riot. Stevenson would go on to lose the election to Eisenhower.
Has there been any primaries candidate that has "unsuspended", i.e. resumed the race after previously announcing a suspension?
An example when this happened with a suspension of several months is Gary Hart's bid for Democratic nomination in 1988.
Hart was the clear frontrunner for the Democratic nomination in the 1988 election. Hart officially declared his candidacy on April 13, 1987.
However, he would suspend his campaign on May 8, 1987, after newspapers had been revealing Hart's extra-marital affairs.
"I said that I bend, but I don't break, and believe me, I'm not broken. (...) Clearly, under the present circumstances, this campaign cannot go on."
He stayed away from the campaign trail for 7 months, until
In December 1987, Hart returned to the race, declaring on the steps of New Hampshire Statehouse, "Let's let the people decide!"
However, the people wouldn't decide in his favor.
After the Super Tuesday contests on March 8, in which he won no more than 5 percent of the vote, Hart withdrew from the campaign a second time.
Finally Michael Dukakis became the Democratic nominee, and lost in the general election to Republican George H.W. Bush.