Sen. Hillary Clinton, D-N.Y., would bring a trove of foreign-policy knowledge and global star power to the job of America's top diplomat, but world leaders would have to wonder if she really speaks for her president, say some Washington insiders. "If she's a person with her own trajectory, how loyal can she be?" said one unnamed official. The best secretaries of State have been very close to the boss, experts say. Some worry President-elect Barack Obama may try to keep control of foreign affairs concentrated at the White House, while others say Clinton may try to build her own power base.