t was 2005, and Felix Sater, a Russian immigrant, was back in Moscow pursuing an ambitious plan to build a Trump tower on the site of an old pencil factory along the Moscow River that would offer hotel rooms, condominiums and commercial office space.Letters of intent had been signed and square footage was being analyzed. “There was an opportunity to explore building Trump towers internationally,” said Mr. Sater, who worked for a New York-based development company that was a partner with Donald J. Trump on a variety of deals during that decade. “And Russia was one of those countries.”