Everyone hear that? That was the $32.5 million sound of Sen. Hillary Rodham Clinton's inevitability melting away in the summer heat. Clinton aides can talk about polls, endorsements, and even trot out (as they are today) the single most popular Democrat on the planet, but that ignores the inconvenient fact that no actual human being has technically voted yet. As for some other measurements -- energy, enthusiasm, and (of course) financing, the edge at this mid-year moment belongs to Sen. Barack Obama, D-Ill.

Obama brought in a cool $10 million more than Clinton did in primary dollars during the second quarter -- a gap greater than former senator John Edwards' entire fund-raising haul for the three-month period. Clinton, D-N.Y., is also raising astronomical sums, and Edwards, D-N.C., is attracting enough cash to stay in the game, but something very real is powering the Obama campaign.

By the eye-popping numbers: Obama brought in more than $32.5 million in 90 days -- all but $1.5 million of it earmarked for the primaries -- for a six-month haul of $58 million, from 258,000 different donors. Forgetting for a moment the unavoidable (and instructive) comparisons to Howard Dean, in a word, Wow. "Obama's fundraising pace puts his candidacy on a course to match and possibly exceed the resources available to Clinton, a former first lady who came to the campaign with extensive ties to the Democratic establishment and a ready-made donor base," write Mike Dorning and John McCormick of the Chicago Tribune.

This is the backdrop ready for former President Bill Clinton upon his return to the campaign stage today. With much of the field hitting Iowa this week, he'll be there with his wife for a four-day campaign swing that starts tonight with an 8:30 pm ET rally at the Iowa State Fairgrounds.

If this does bring a boost (and realize how little attention there is these days to the downside of putting the former president on the trail), the Clinton campaign needs it: The leader in national polls already had an Iowa problem, and now she has an Obama problem that runs deeper than dollar signs. "Hillary Clinton may be the one consistently coming out top when Democratic voters are asked who they want to be their presidential candidate, but Barack Obama seems to be the one they reach into their wallets for," write Politico's Ben Smith and Richard Allen Greene.

One final point illuminated by the numbers: The Democratic field looks like it has three tiers now -- Obama and Clinton at the top, Edwards and Gov. Bill Richardson, D-N.M., in the next grouping, and everyone else bringing up the rear. Edwards reported topping $9 million for the quarter (meeting his publicly stated goal) while Richardson brought in $7 million --

respectable sums that were eclipsed by the top tier. The Edwards and Richardson camps say they are on track to compete in the early-voting states, but all the candidates are being lapped by Obama and Clinton. "An important subtext arising from the latest round of fund-raising reports is the growing distance between Mr. Obama and Mrs. Clinton and the second-tier candidates," writes The Wall Street Journal's Brody Mullins.