The Pentagon has abruptly scrapped plans to deploy a brigade of 4,200 U.S. troops, which make up one of the Army’s frontline tank formations, to Poland, according to five U.S. officials. The move would cut the American combat power in Poland by nearly half.  The Army’s 1st Cavalry Division, 2nd Armored Brigade Combat Team, based at Fort Hood, Texas had been slated to replace another armored unit from the same division that deployed to Poland last year.  The move came as a surprise both inside the unit and among defense officials and lawmakers. Preparations for the deployment were already well underway with the brigade having shipped much of its equipment and advance personnel into Europe, a routine step in large-scale military movements that sends troops and gear ahead of the main force. Sen. Jeanne Shaheen, D-N.H., the ranking member of the Senate Foreign Relations Committee, told reporters she was concerned.…