The day that Mr. Biden and his team had feared for more than three months came on January 28, when an attack by Iranian-backed groups left American soldiers in Jordan bleeding.

Biden will now have to decide how far he is willing to retaliate to avoid sparking a wider war in the Middle East, a prospect he has tried to avoid since Hamas’ October 7, 2023, attack on Israel.

3 months of tightrope walking

Over the past three months, President Biden has been very cautious in choosing how to respond to more than 150 attacks by Iran-backed militias on US forces in the Middle East.

Biden has essentially not responded to the vast majority of attacks that were successfully thwarted or caused little damage, while ordering limited responses to more daring attacks, particularly by Houthi forces in Yemen.

But what remains unclear is whether Mr Biden would order strikes on targets inside Iran, as his Republican critics have urged.

“The question facing Biden is whether he simply wants to react to events in the region, or whether he wants to send a larger message to try to restore deterrence that has been absent in the region for months,” Brian Katulis, a senior fellow at the Middle East Institute, told the New York Times .

Mr. Katulis commented that the White House is looking for a response that is not so tough as to provoke all-out war, but not too soft.

Speaking to the New York Times, a senior US official revealed that Washington does not currently believe that Iran intends to start a larger war through the attack in Jordan. However, the analysis is not yet finished.

A broader conflict could serve Iran’s purposes, but US officials have long believed Tehran understands the high cost that could come from a direct war with the US.

Complicating Mr Biden’s decision is that increased aggression against Iran could make it more difficult to end the fighting in Gaza.

The Blames

"The whole world is watching for signs that President Biden is finally ready to use American power to force Iran to change its behavior," said Senator Mitch McConnell, the Republican leader in the Senate.

Republican Senator Lindsey Graham put it more bluntly: "Hit Iran now. Hit it hard."

For his part, Mr. Trump claimed that “this attack would never have happened if I were president, not even a chance.” But in fact, Iran and its proxies continued to attack American and allied facilities during Mr. Trump’s presidency, and at times he called off a retaliatory strike that he considered excessive.

Mr Biden has given no indication of his views yet, but he has vowed to take action.

“We had a tough day last night in the Middle East,” Biden told a crowd at an event in South Carolina on January 28. “We lost three brave souls in an attack on one of our bases.”

After a moment of silence, he emphasized: "And we will respond."