US correspondent James Matthews said: Regarding retaliation, the question for Joe Biden will be how “huge” it has to be.
So far, we have seen a measured U.S. response to the attack, facilitated by the fact that no American lives were sacrificed.
That has changed.
The death of a U.S. service member is above all a tragedy for those involved and represents an affront to America's sense of global authority and influence over world events.
This raises questions about Biden's judgment and amplifies criticism that he has been too restrained in his response to the relentless invasion.
His challenge is to look beyond his next move.
Presidents involved in the region, friends and foes alike, will know in advance how far retaliation will need to go.
The United States will look to human and technical intelligence to establish whether there was direct involvement and direction by Iran.
The same information has led U.S. officials to believe, at least until now, that Iran does not want direct conflict with the United States and recognizes the danger it poses.
However, Tehran has not been troubled by the proxies' operations. That's the problem Biden needs to address.
In doing so, we will see whether his principles on retaliation apply not only to allies but also to America itself.
Video: How should the US respond to the strikes? Wilfred Frost hears from security analyst Jonathan Parris…