Finally, the two candidates leading the Democratic presidential field this summer, Hillary Rodham Clinton and Barack Obama, have engaged one another in the first significant test of their campaign combat skills. But the most amazing thing about their war of words last week is that she started it a surprising move for an increasingly clear front-runner whose campaign has so far been most notable for avoiding risk.

Even at this relatively early stage, six months before the first votes are cast, deconstructing the Clinton-Obama smackdown provides a telling preview of what’s to come when more voters are paying attention. Essentially, the two camps are eyeing each other like competitors in the early rounds of a boxing match, carefully judging the angle and force of each punch and counterpunch.

Clinton uncharacteristically gambled with some fighting words in calling Obama “irresponsible” and “naive” for saying — during the debate sponsored by YouTube and CNN — that as president he would unconditionally meet with Cuba’s Fidel Castro and other dictators around the world. The New York senator risked putting the spotlight on a contender who was drifting down in the polls without her help.

And it served to give the Illinois senator a platform for razzing Clinton about her support for going to war, which he opposed. Obama took less than a day to return fire, saying the real naivet?? and irresponsibility were displayed in Clinton’s original vote to authorize the invasion of Iraq “without asking how we were going to get out.” He stood his ground on his plans to remain open as president to talking with enemy dictators, portraying that approach as a needed change from the unyielding belligerence of Bush administration foreign policy.

Why would Clinton, who’s been comfortably ahead in every recent poll, risk the potential boomerang effect of such an attack just as Obama’s popularity balloon was gradually deflating on its own? Her advisers privately suggest that the maneuver was less about hurting Obama and more about the Clinton camp’s current focus on the male voters resisting her candidacy — which also would explain her recent high-profile spat with the Pentagon over Iraq War policy. The idea is that, while Clinton builds on a strong lead among women, she is looking for ways to impress men by demonstrating toughness on high-stakes issues.

The Obama team insists the Clinton attack backfired, offering him a chance to counterattack without taking on criticism for the politics-as-usual negativity he’s vowed to avoid. And they relished the chance to ding Clinton once again for her war vote.

With both candidates claiming victory in that confrontation, the stage is set for plenty more. If each side believes it’s landing the better punches, why would either one stop?

The Clinton forces have long been frustrated by Obama’s meteoric rise and his ability to leverage that phenomenon into a slight lead in campaign cash — a surprising development that complicates her aim to come off as invincible. At this stage in the campaign, Clinton’s main objective with regard to Obama is to seed doubt about his readiness for the Oval Office. Obama’s camp believes that he benefits whenever the race comes across as a one-on-one contest against Clinton. That serves to crowd out the rest of the field and pave the way for him to consolidate the “anyone but Hillary” vote.

The other Democratic contenders have every reason to cheer Clinton on against Obama. None see an opportunity to upset her lead without first displacing Obama as the principal alternative.

A firm rule in politics is that a candidate in the middle of the pack (or worse) must take aim first at the closest rival in front — and, if successful in eclipsing that person, keep knocking off the next people up the pecking order until the front-runner is the only rival left. That’s a rule that John Edwards seemed to follow in the fallout over Obama’s vow to meet with dictators. The former North Carolina senator echoed Clinton’s criticism of Obama’s willingness to talk to sworn U.S. enemies — because Edwards knows that an Obama stumble can help him get closer to Clinton.

Obama most likely weathered this storm without losing the alternate slot. But it’s not yet clear whether the spat will help cut down Clinton’s mounting lead — ahead of Obama by double digits in numerous national polls, and well ahead in both Iowa and New Hampshire.

Obama’s campaign told reporters that focus-group polling of Democratic primary voters revealed an appreciation for his openness to international dialogue. But the Clinton camp saw a boost in the electorate’s view that her experience trumps Obama’s message for change. Experience vs. change is destined to be the prevailing dynamic of Clinton vs. Obama. And the mixed results of last week’s dust-up showed that each has the skill to make that contest too close to call.

Contributing Editor Craig Crawford is a news analyst for NBC, MSNBC and CNBC. He can be reached at ccrawford@cq.com.