In an article today, I note that Mitt Romney's trip to Europe and Israel is being treated as entirely normal thing for him to do, while only four years ago, Barack Obama's mid-campaign overseas tour was considered a bizarre and unprecedented stunt.
Prior to 2008, the main example I could find of a candidate heading abroad as part of a presidential campaign was George McGovern's 1971 diplomatic mission to Vietnam, which served mainly to give him a platform to blast the Nixon administration's handling of the war.
However, according to this blog post by Eric Ham of the XII Project, there may be another precedent:
Presidential candidates traveling abroad while also campaigning for the presidency is not a new phenomenon. In fact, these excursions, date back to as far as 1947 when Republican presidential frontrunner, Harold Stassen, took a two-month 18-country tour around Europe in the spring of that year.
Stassen, a former governor of Minnesota, is best known for having unsuccessfully run for president nine times between 1948 and 1992. The 1948 primary, which he lost narrowly to Thomas Dewey who eventually lost to Harry Truman, was the closest he ever came to the Oval Office.
There's doesn't seem to be much information online about Stassen's trip or his itinerary, except for this transcript of an April 9, 1947 conversation with Joseph Stalin. Sample:
Stassen: Generalissimo Stalin, on this European trip I am particularly interested in studying conditions of an economic nature. In this regard, of course, the relations of the U.S.A. and the U.S.S.R. are very important. I realize that we have two economic systems that are very different. The U.S.S.R. with the Communist Party and with its planned economy and socialized collective state, and the United States of America with its free economy and regulated private capitalism are very different. I would be interested to know if you think these two economic systems can exist together in the same modern world in harmony with each other?
Stalin: Of course they can. The difference between them is not important so far as co-operation is concerned. The systems in Germany and the United States are the same but war broke out between them. The U.S. and U.S.S.R. systems are different but we didn’t wage war against each other and the U.S.S.R. does not propose to. If during the war they could co-operate, why can’t they today in peace, given the wish to co-operate? Of course, if there is no desire to co-operate, even with the same economic system they may fall out as was the case with Germany.
So much for that idea.