Signaling a possible shake-up among President Bush's senior advisers, the new White House chief of staff told top presidential aides Monday to expect changes to "refresh and re-energize the team." He invited anyone thinking of leaving before year's end to do so now. Joshua Bolten, who took over the top staff job late Friday, asked for no one's resignation in his first Monday morning staff meeting with the president's senior aides, presidential spokesman Scott McClellan said. Likewise, nobody offered to leave, McClellan said. Bolten has Bush's full authority to make changes to the president's staff, which has had a low turnover rate as many aides have served him for years. Bolten already has had private meetings with some top advisers and plans more in the coming days, McClellan said.