Yes, an isolationist would be supported in an election, because Americans are sick of going to war. George Washington warned in his farewell address that it's very important to stay out of international affairs. LBJ ran for office on an isolationist platform and won. Ronald Reagan avoided going to war. Depending on where we are at in history, an isolationist is supported in office.
In the United States, an isolationist would definitely receive support in elections. More and more Americans feel like we should separate ourselves from the rest of the world as much as possible. A decent amount of people would support such a candidate, although victory in an election would be unlikely.
Americans would definitely support an isolationist, as so many people espouse these beliefs already without calling them such. The problem here is that people are completely blind to how much of our economy and way of life revolves around foreign trade and import/export, far more than would be made up in domestic job creation.
Isolationism is a category of foreign policies institutionalized by leaders who asserted that their nations' best interests were best served by keeping the affairs of other countries at a distance. Depending on the person, they may have a chance at getting elected. However, we profit as a nation by some of the contracts that we have on other countries soils so I do not know how that would work. We could definitely use someone that would put the problems of the United States first before trying to save another country.
I don't think in a recent election that an isolationist would be supported by a majority of the country. This is not a policy that most of the country agrees with so I don't think they would support him in any real election. Maybe in a few more years, but not now.