Secretary of State Colin Powell (2001-2005).
Powell supported Bush administration's decision to invade Iraq after the failure to find diplomatic alternatives, and has been consistent in his position on U.S. involvement in the Iraq War even after President Obama's election.
However, Powell made his best efforts to convince President Bush that the U.S. needed to appeal to the United Nations first, and was skeptical whether the U.S. had enough troops to successfully carry out the operation meant to suppress violence and end the civil war in Iraq.