A member of the Iraqi security forces fights in a village near the city of Ramadi, which is held by the Islamic State. (European Pressphoto Agency)

There are certain ground truths about dealing with the Islamic State in Syria and Iraq that leading U.S. politicians don’t want to accept.

I am not talking about the notion, for instance, of Sen. Ted Cruz (R-Tex.), whose announced approach is: “We will carpet-bomb them into oblivion. I don’t know if sand can glow in the dark, but we’re going to find out.”

What I am concerned about is those who should by now know better but continue to rip into President Obama’s strategy of discreet bombing of Islamic State targets coupled with training and equipping local forces on the ground.

One major new argument, since the horrendous terrorist killings Dec. 2 in San Bernardino, Calif., is that haste is needed to seize Raqqa, the group’s de facto capital in Syria, and crush the Islamic State leadership to prevent further attacks within the United States.

Of course, so far there is no proof the Islamic State leadership was directly connected with Syed Rizwan Farook and Tashfeen Malik, the couple who carried out the San Bernardino attack. They apparently swore allegiance to the Islamic State’s leader only immediately before their attack.

That did not stop Sen. John McCain (R-Ariz.), chairman of the Senate Armed Services Committee, from telling Defense Secretary Ashton B. Carter on Wednesday at a committee hearing that as long as the Islamic State has a “caliphate base [in Raqqa], then they are able to orchestrate attacks such as they have successfully achieved in the last several weeks, whether it be . . . Ankara or the Russian airliner, southern Beirut, Paris or San Bernardino.”

McCain wanted to know how long it would be before “we retake Mosul [a major city in Iraq captured by the Islamic State in June 2014] or Raqqa.” He said: “Here we are with attacks on the homeland, the United States of America. We have not contained ISIL [the Islamic State], and we have no timeline . . . and there is no plan, no strategy to retake Raqqa.”

McCain said the United States could “with a large Arab force . . . go in there and take those people out.”

“They are not giants,” he added.

McCain made putting together a multinational force sound simple, saying that, based on his conversations in the area, meaning Sunni and Arab leaders “are willing to do so if there is a United States commitment.”

Carter responded that his past “lengthy conversations” had shown that it is very difficult. But he will have another chance soon, since Obama sent him Monday to the Middle East “to work with our coalition partners on securing more military contributions to this fight.”

An example of ground truths that shows just how difficult it will be to retake Mosul and Raqqa can be seen in a Pentagon briefing Thursday by Col. Steve Warren on video from Baghdad.

Taking questions from reporters, he described the fight to retake the Iraqi city of Ramadi. The capital of Sunni-dominated Anbar province, Ramadi was once a city of 190,000. It was taken by Islamic State fighters in May, and today the population may be about 10,000. Warren estimated there may be 600 to 1,000 Islamic State fighters remaining in Ramadi, with another 350 killed. The city is surrounded by Iraqi forces, but it is taking a combination of Iraqi army elements, an elite Iraqi special forces unit, some Sunni militias and U.S. and allied bombing to retake the city. It still could take weeks.

Warren described why. He said that the Islamic State “has had a long time to prepare these buildings [in Ramadi]. They’ll knock holes in walls between two adjacent buildings so they can move from building to building undetected. We’ve seen them do things like put sheets up over roads or alleyways so that they can move up and down a road or alleyway without being detected.” The militants have placed booby-trapped mines throughout the city that, “combined, allow a relatively small force to be able to hold off a substantially larger force,” Warren said.

Transfer that ground truth to Mosul, a city that had a population of more than 1 million before the Islamic State took over in June 2014 and now is down to about 600,000. One step toward retaking the city occurred recently when combined Arab and Kurdish forces, with U.S. bombing support, cut the main supply route between Raqqa and Mosul. Asked Wednesday by McCain how long it would be before Mosul could be retaken, Carter answered frankly: “It is hard to say, because it depends much on the progress of the Iraqi Security Forces, which I described as building themselves into a more capable combat force.”

Raqqa, a city of some 200,000 in northern Syria, is flooded with foreign fighters and an even harder case.

Gen. Paul Selva, vice chairman of the Joint Chiefs of Staff, testified last week along with Carter. Speaking about plans for Raqqa, Selva said moderate Syrian opposition forces so far are not large enough to take and hold the city. One reason for adding U.S. Special Operations forces to Syria was “to build that depth of intelligence to understand which forces are available to put increasing pressure and a hold force into Raqqa,” he said.

McCain and his colleagues should understand that, as Obama said Monday, “this continues to be a difficult fight. . . . ISIL is dug in, including in urban areas.” So while the United States continues its precision bombing, “our partners on the ground are rooting ISIL out town by town, neighborhood by neighborhood, block by block.”

The ground truth is this all takes time.