WASHINGTON, Jan. 10 — By stepping up the American military presence in Iraq, President Bush is not only inviting an epic clash with the Democrats who run Capitol Hill. He is ignoring the results of the November elections, rejecting the central thrust of the bipartisan Iraq Study Group and flouting the advice of some of his own generals, as well as Prime Minister Nuri Kamal al-Maliki of Iraq.

In so doing, Mr. Bush is taking a calculated gamble that no matter how much hue and cry his new strategy may provoke, in the end the American people will give him more time to turn around the war in Iraq and Congress will not have the political nerve to thwart him by cutting off money for the war.

The plan, outlined by the president in stark, simple tones in a 20-minute speech from the White House library, is vintage George Bush — in the eyes of admirers, resolute and principled; in the eyes of critics, bull-headed, even delusional, about the prospects for success in Iraq. It is the latest evidence that the president is convinced that he is right and that history will vindicate him, even if that vindication comes long after he is gone from the Oval Office.

Mr. Bush long ago staked his presidency on Iraq, and to the extent he can salvage the war he can also salvage the remaining two years of his administration. So he is taking a risk, challenging not only the Democratic leadership in Congress but also some members of his own party, who are openly skeptical that the new policy will work and who, unlike the president, will be running for re-election.