In recent months, an Iranian nuclear scientist as well as a top Hezbollah official were killed. Iran blames Israel and they're probably right. Over the weekend, Israeli citizens associated with embassies in New Delhi and Tbilisi, Georgia were unsuccessfully targeted by bombers, thought to be Iranian.
If you consider the ramping up of violence on each side, against the backdrop of a possible nuclear Iran being in such close proximity with the "Zionist state" as they like to call Israel, you can envision nothing but trouble ahead.
In addition, Saudi Arabia is saying that if Iran completes its nuclear weapons development program, it will do the same thing to prevent Iran from establishing a nuclear hegemony in the region. The US and some others are applying pressure to the Iranian regime through boycotts and embargoes, but they won't work as long as Russia and China continue to deal with Iran.
I guess the US's role in the eventual hostilities between Iran and Israel will be determined by what kind of conflict takes place. If it's just a surgical strike on Iran's nuclear facilities, I doubt we'll do anything. But what if Iran decides to retaliate with a ground attack on Israel? Do we jump in and come to Israel's defense or let her fend for herself? I don't think Iran will attack Israel first. Ahmadinejad is posturing, using the guise of peaceful energy development, so that Israel is compelled to attack first, affording Iran with sympathy from the world community.
Anyway it plays out, the US doesn't need to get into yet another theater of conflict in the middle east. Hell, by then we'll probably be overthrowing the Syrian regime. The last thing we need to do is exactly what the neocons want us to do which is be quick to get into a fight with Iran.