If you don't have anything at all to say, don't say something nice.

It's an inviolable law of presidential politics: the closer two rivals for office are on the issues, the nastier the tone of the campaign. Exhibit A, of course, was the endless Democratic primary clash between Barack Obama and Hillary Clinton, who, as Obama once put it, "agree[d] on 98.9 percent of the issues" but still managed to spend 16 straight months fighting over the other 1.1. percent. Now it seems John McCain has found himself in a similar pas de deux with Obama on Iraq. For months, the Democratic nominee has advocated a rough 16-month timetable for withdrawal, and for months, his Republican rival has said such a schedule would amount to "surrender." That was a fertile ground for debate. But last week the White House announced that President Bush and Iraqi Prime Minister Nouri al-Maliki had agreed on the idea of a "time horizon" for withdrawing American troops, and Maliki told German newsmagazine Der Spiegel that U.S. troops should leave "as soon as possible, as far as we're concerned." "U.S. presidential candidate Barack Obama talks about sixteen months," he said. "That, we think, would be the right time frame for a withdrawal, with the possibility of slight changes." All of which forced McCain to admit, in an interview Friday with CNN, that 16 months is a pretty good timetable." In other words, vamanos.

This kind of consensus may be good for the country. But unfortunately it's bad for McCain's campaign. Without any substantive distance between him and Obama on the way forward in Iraq, the Arizona senator has chosen to indulge in recent days in a series of meaningless attacks meant create the illusion of contrast where none actually exists. First is the issue of contingency. Speaking to CNN, McCain was careful to affix an "[as long as] it's based on conditions on the ground" disclaimer to his approval of a 16-month timeline--the implication being that only he (and not Obama) will factor those conditions into his withdrawal calculus. And when Obama told my NEWSWEEK colleague Richard Wolffe Friday that the size of his residual force--which would stay in Iraq after combat troops withdraw to assist with intelligence, counterterrorism and training--would be "entirely conditions-based," McCain acted as if his rival had experienced some sort of epiphany. "Today Barack Obama finally abandoned his dangerous insistence on an unconditional withdrawal of U.S. combat troops from Iraq by making clear that for the foreseeable future, troop levels in Iraq will be 'entirely conditions-based,'" said McCain spokesman Tucker Bounds. "We welcome this latest shift in Senator Obama's position."

The only problem? There wasn't any shift. Truth be told, Obama has always been open to adjustments when it comes to residual forces--even if McCain thinks it convenient to claim otherwise. At a Democratic debate in Hanover, N.H. on Sept. 26, 2007, for example, the late Tim Russert pressed Obama as to whether he would have all troops out by the end of his first term. "I think it's hard to project four years from now, and I think it would be irresponsible," Obama said. "We don't know what contingency will be out there. I will drastically reduce our presence there to the mission of protecting our embassy, protecting our civilians and making sure that we're carrying out counterterrorism activities there. I believe that we should have all our troops out by 2013, but I don't want to make promises not knowing what the situation's going to be three or four years out." In other words, conditions mattered to Obama then--and they still matter now. Only the wildest partisan would believe that Obama ever planned to stick to his 16-month timetable no matter what the military brass said, no matter what was happening on the ground and no matter what sort of trouble it would create for American soldiers.

Without even this illusory policy difference to flog, McCain had to find another line of attack. His chosen course, as Politico reports this morning, is "to employ the tack many strategists see as essential and which anonymous e-mailers and commenters with no apparent links to his campaign have been practicing since last summer: hitting Obama not on his record or his platform, but on his values and person." McCain's new strategy is on full display in his latest ad, "Troops (video above), which slams Obama for, among other things, "ma[king] time to go to the gym, but cancel[ing] a visit with wounded troops" because "the Pentagon wouldn't allow him to bring cameras." McCain's goal here is clear: to paint Obama as an unpatriotic troop-hater. Unfortunately, the accusation is baseless.

It's true that in Germany last week Obama went to the gym and nixed a trip to Landstuhl Regional Medical Center. But any resemblance to reality ends there. Late last week, the Pentagon informed Obama that it would regard the foreign policy adviser accompanying him to Landstuhl, Maj Gen. Scott Gration (Ret.), as a campaign staffer. Worried that the visit would be seen as a photo-op, his team called it off. "The last thing that I want to do is have injured soldiers and the staff at these wonderful institutions having to sort through whether this is political or not or get caught in the crossfire between campaigns," the candidate told reporters last week. In other words, he was afraid that the political spotlight would shine too brightly on the event--not, as McCain alleges, that it wouldn't shine at all. (Landstuhl--like the Combat Support Hospital Obama visited in Iraq--was simply never on the traveling press corps' schedule.) This may expose an excess of caution and concern over appearances. But it doesn't make Obama a troop-snubber. Meanwhile, McCain spent much of the weekend sniping that his rival "would rather lose a war in order to win a political campaign"--a line that Joe Klein called the most "intemperate... personal attack... I've ever heard a major-party candidate make in a presidential campaign, and the sort of thing that no potential President of the United States should ever be caught saying."

As I've written before, McCain was right about the surge, and Obama, who claimed that violence would increase, was wrong. Thanks to Gen. David Petraeus's counterinsurgency strategy and the simultaneous "Sunni Awakening," Iraq is far more stable today than it was in early 2007--and Obama's 16-month withdrawal plan is far more convincing now than it was then (when death squads were slaughtering 4,000 civilians a month and political progress looked impossible). Judging by his recent comments, McCain seems to concur. Which is why the conventional wisdom--"that [McCain] can make inroads with voters by keeping the focus on foreign policy issues," as Juliet Eilperin reports in today's Washington Post--may no longer reflect reality, at least when it comes to Mesopotamia. As the old disagreements over "what's next" in Iraq have largely dissolved in recent days, McCain's side of the debate has deteriorated into a slop of "I told you so" taunts, willful distortions and thinly veiled assaults on Obama's patriotism. And like any message that's mostly negative, mostly retrospective and literally unbelievable--does any objective observer really think Obama hates the troops?--the potential for backlash is big. "It's churlish and unlike McCain, and hardly will resonate with the swing voters who are going to decide this election," a leading Republican strategist told the Post this morning. "They're doing it because the candidate, and the campaign, is not happy with where they are and they're lashing out." The question facing voters this fall isn't who was right on the invasion (polls say Obama), who was right on the surge (polls say McCain) or even who has the best plan for getting out (they're virtually indistinguishable). It's who do you want to see as Commander in Chief, on TV, while we withdraw. The angrier McCain sounds, the more tempted America will be to change the channel.