Welcome to Washington, Gen. Petraeus. You had better get used to being called a liar.

Even before Gen. David Petraeus testified before Congress, Democrats launched offensive operations against his credibility. Sen. Dick Durbin, D-Ill., accused him of "carefully manipulating the statistics," and Senate Majority Leader Harry Reid said that he "has made a number of statements over the years that have not proven to be factual." MoveOn.org charmingly called him "General Betray Us" in a full-page ad in The New York Times, capturing the gravamen of the Democrats' attack on him -- that he's dishonestly exaggerating progress so America can keep expending blood and treasure in Iraq.

Why Petraeus would risk his professional reputation with such tawdry lies is unclear. If it were just opportunism, surely this Princeton Ph.D. could have figured out that there were shrewder professional moves than hitching his career to an unpopular war at a time when it seemed well-nigh unsalvageable and at the behest of a president with approval ratings below freezing.

The Democrats are angry at Petraeus because they hate his message so much -- that we have achieved some progress with the surge. This might be the first time ever that a messenger has been shot for bringing a message of good news. Petraeus did it in a sober and careful way, leaving little doubt in his testimony that he has a better command of the war -- and a more realistic appreciation of all its devilish difficulties -- than his congressional interlocutors.

For a man accused of being a partisan liar, Petraeus was resolutely nuanced. He noted that the "situation in Iraq remains complex, difficult, and sometimes downright frustrating." Achieving our objectives will be neither "quick nor easy." But he believes that achieving them is still possible, and a premature withdrawal "would likely have devastating consequences."

It is that conclusion that so infuriates the left. It has no patience for Petraeus' proposal to withdraw the additional surge forces from later this month to July 2008 in a deliberate manner that won't give back security gains that we have made this year and that will hand over responsibility to Iraqi forces only when they are ready. The opposition to the war prefers the simple and simplistic expedient of getting out -- consequences be damned.

Democrats tried to counter Petraeus with cherry-picked evidence, including a Government Accountability Office report saying that it is too hard to measure the trends in violence to make a judgment about them. This bit of epistemological dodginess is being spun by Democrats into an affirmation that the surge didn't reduce violence. But the trend is unmistakable. Michael Gordon reported in The New York Times that both American and Iraqi numbers "note a roughly 50 percent drop in the number of civilians who have been killed since the end of 2006."

Democrats also point to a commission report on the Iraqi Security Forces prepared under the direction of retired Gen. Jim Jones. It says that Iraqi forces won't be able to operate independently in the next 12-18 months. This is true, and unsurprising. The Iraqi military was designed as a light infantry capable of quickly getting into the fight and dependent on our logistics. The report nonetheless expects "substantial progress" in Iraqi forces in the next 12-18 months.

In the context of Iraq, Democrats are practically allergic to the word "al-Qaida." The terror group has almost been rousted from Anbar province -- once the epicenter of the Sunni insurgency -- but Democrats love only to note that Anbar has 5 percent of Iraq's population. Do they care that at times Anbar accounted for one-third of American casualties?

The Democrats' posture toward Petraeus said implicitly, "Don't distract us with your encouraging news and your measured policy recommendations." On Iraq, they want to hear of defeat and withdrawal. An accomplished military professional who brings a message of success and patience is to be, at best, dismissed and, at worst, smeared.