Well, Iran has been organizing, training, and equipping proxy forces to attack US personnel for decades. They also launched IRBMs at US forces a couple years back. They had also been blaming us for Israeli strikes and threatening more action. Not sure how much this will really increase the threat level... probably some, but not exactly 0 to 100.
Deciding when to use military force is also the job of the President (codified since the War Powers Act).