But, first, as we know Robin would have insisted, the news.

Warning signs are flashing red throughout the Middle East and beyond tonight, as Israel and the U.S. await a possible Iranian response to the attack on its consulate last week in Damascus, Syria.

That Israeli airstrike killed one of Iran's senior military leaders, and the Islamic Republic has vowed vengeance.

Following it all is Nick Schifrin, who joins us now.

It's good to see you, Nick.

So how great is the concern, and what exactly are the U.S. and Israel bracing for?

NICK SCHIFRIN: A senior administration official tells me tonight that the concern is -- quote -- "very high."

U.S. and Israeli officials are preparing for strikes by Iran and Iran's proxies inside Israel.

And Iran, Geoff, has never attacked Israel with kinetic weapons before.

One U.S. official tells me the attack is likely to be -- quote -- "bigger than usual."

Another U.S. official tells me the timing of the attack could be -- quote -- "by the end of the weekend."

But I will say that another official from a different branch of government is telling me that the assessment is more that Iranian proxies by themselves would attack Israel or its assets in the region.

And so, clearly, there are ongoing assessments of what could happen.

But all the officials agree that the most likely scenario we're talking about is Iranian missiles or Iranian-made missiles and drones attacking inside Israel and/or attacks on Israel outside of Israel property.

And to show how seriously the U.S. is taking this, the U.S. Embassy in Israel yesterday announced that U.S. government employees and their families would be restricted from traveling outside of Jerusalem, Tel Aviv, or the southern city of Be'er Sheva.

Those are the places, by the way, that Israeli Iron Dome and missile defense are strongest.

And today, President Biden said an attack would be -- quote -- "sooner than later."

QUESTION: What is your message to Iran in this moment?

JOE BIDEN, President of the United States: Don't.

We are devoted to the defense of Israel.

We will support Israel.

We will help defend Israel.

And Iran will not succeed.

NICK SCHIFRIN: The show of U.S. military support came most visibly today from General Erik Kurilla, commander of U.S. Central Command.

You can see him there on the left.

He oversees all U.S. troops in the region.

He met with Israeli Defense Minister Yoav Gallant.

And Gallant said that the two of them discussed -- quote -- "readiness" for an Iranian attack against the state of Israel.

As for Iran, Geoff, it has made very clear it will respond to Israel's attack on Damascus, including a threat posted on the Web site of Supreme Leader Ali Khamenei.

AYATOLLAH ALI KHAMENEI, Supreme Leader of Iran (through translator): Attacking our consulate is like attacking our soil.

This is commonly agreed around the world.

The malicious regime has made a wrong move in this case.

It should be punished, and it will be punished.

(CHEERING AND APPLAUSE) NICK SCHIFRIN: You see the cheers there, Geoff.

It all adds up to a very tense moment in the region.

GEOFF BENNETT: Does the U.S., Nick, expect an attack on U.S. assets in the region?

NICK SCHIFRIN: The short answer is no.

Multiple U.S. officials tell me they do not expect an Iranian attack on U.S. troops in the region.

In the words of one official, they expect a -- quote -- "calibrated attack," not to draw the U.S. into war.

And a defense official tells me tonight the U.S. is preparing defenses and has moved additional military assets in the region, and they won't go into detail on what exactly the U.S. has moved.

But the U.S. and its allies are also emphasizing that they are trying their best to use diplomacy in this moment.

The U.S. has indirect channels with Iran, mostly through the Swiss Embassy in Tehran and the Iranian mission at the United Nations, and it can pass messages that way.

And British, German and French officials have all met with senior Iranian leaders just in the last few days.

And each of those countries' officials are saying to reporters here in Washington, but also in their capitals, that they have sent messages of restraint.

But the bottom line is, ever since the Damascus strike, U.S. and Israeli officials have said that the Iranian response is all but inevitable.

They have to respond, given that the targets that officials believe Israel killed were so senior in the Iranian Revolutionary Guard Corps.

It's just a question tonight, Geoff, of how far Iran goes and, of course, how Israel responds to what Iran does.

GEOFF BENNETT: Well, we will wait and we will watch.

Nick Schifrin, thanks to you for that great reporting.

NICK SCHIFRIN: Thank you.