Sen. Tom Harkin says the fact that he got 79 percent of the vote in Iowa's Democratic caucus shows that the people who know him best give him strong support. His opponents' supporters say the fact that only 25,000-30,000 Democrats turned out, compared to 126,000 four years ago, shows that he has no drawing power. They're both wrong. Iowa proved nothing, as usual. At this stage of the campaign, primaries are the only way to measure candidates' true strength. It is worth remembering that in 1988, George Bush came in third in the Iowa Republican caucus, and Michael Dukakis came in third in the Iowa Democratic caucus. The real campaign starts Tuesday in New Hampshire.