Despite the victory of the Democrats in both houses of Congress, Trump still has a lot of power to carry out his decisions. The President of the United States can veto congressional approvals, and Democrats need a two-thirds vote of both houses to override the veto. It is very difficult considering the number of seats. Therefore, Trump can still order a military attack on Iran, and in many situations, he does not need prior approval from Congress to begin military operations. Democrats can make it harder to continue the war with political pressure, limiting the budget and government oversight, but they can't stop Trump's military decision simply by taking over Congress.