President Bush will "have to make a decision" regarding U.S. troops levels, the Virginia senator and senior Republican on the Armed Services Committee said on NBC's "Meet the Press." Congress will evaluate Bush's decision and "we'll have to make our decision as to what we do."

"I don't say that as a threat, but I say that is an option we all have to consider," said Warner, who recently returned from Iraq.

U.S. troops "have performed magnificently," he said, but Iraqi Prime Minister Nouri al-Maliki and other Iraqi leaders "have totally failed" on their side of the partnership, namely to "deliver greater security and reconciliation."

"Because of this, military support must be re-evaluated," he said.

Senators could consider "some type of troop program taking away from the president ... his constitutional power to make those decisions," he said.

Warner said the Senate would wait until after a September military update on the situation and Bush's response to it.

"After he speaks, then we'll have to make our own assessment," Warner said.