If you want a good illustration of the difference between a necessary and a sufficient condition, look at John Podhoretz's article over at Contentions on why Mike Huckabee is not a shoe-in for the Republican nomination for president. Here is the essence of Podhoretz's argument:
The Christian base of the Republican party is unquestionably important. It may make up as much as 35 percent of the primary vote. If Huckabee wins a landslide majority of evangelical votes nationwide, say 65 percent, he will have in his pocket one-fifth of the Republicans participating in the primaries. That’s a very significant number in a populous and divided field.
...The problem Huckabee faces as he moves into the first tier is that, aside from his very pleasing demeanor, he is not giving any other kind of Republican — a national-security Republican, a small-government Republican, a low-taxes Republican — any reason whatever to vote for him. Everyone understands you can’t win without the base. But the obsession with winning the base can blind some people to this basic fact: A man cannot win by base alone.
In other words, winning the base is a necessary, but not a sufficient condition for winning the nomination.
This is a persuasive argument, but there are so many intangible factors in politics, such as the force of sheer momentum--and the smell of a winner. Huckabee's economic views may not be conservative (which is why I'm for Thompson), but they are populist. And a win in Iowa gives him the glow not only of success, but the appearance of political velocity: he is elevated from a 2nd tier to a 1st tier candidate, and is on his way up.
