Russia’s invasion of Ukraine has lasted nearly a month but Moscow’s forces remain stalled, said a Pentagon official on Tuesday. “We have assessed, for the first time, that the Russians may be slightly below a 90 percent level of assessed available combat power,” a senior Department of Defense official told reporters, according to a transcript released by the agency. The official, who requested anonymity, said that it “is of the combat power that they assembled in Belarus and in the western part of their country prior to the invasion” and  “is not an assessment of all Russian military power.” Before the Russia-Ukraine conflict started on Feb. 24, there were estimates that more than 150,000 Russian troops were massed along Ukraine’s borders in Russia and in Belarus. The Belarussian military is not involved in the conflict, although some Ukrainian officials believe Belarus may invade in the near future. There is also …