[GK3]

Similarly, Iran so far has been able to do whatever it wants through it's proxy forces in much of the middle east. Eventually, they will go "too far" and either Israel or the US will take military action. We need a way to let Iran know this can't go on. We don't have that AFAIK. That is the danger. Starting a war and occupying Iran is possible. Then what?

If the deaths of American military personnel isn't "too far", and the ongoing attacks by Houthis and others isn't "too far", then...what would constitute "too far"?

I obviously don't know exactly what constitutes a "red line" for the administration, but I think the correlation of forces is something like the following: The Iranians will respond to any killing of ethnic Iranian forces (e.g. the Quds force) in other countries (Iraq, Syria, Jordan, Lebanon, etc.) with like actions in the same area. The US does the same. That means that both Iranian and US personnel die in the middle east and no war is declared as a result. If the US attacks the territory of Iran, that will start a war. If a terrorist attack happens on US soil that can be traced to Iran, IMO that will result in the US striking Iran heavily and that will start a war. Anything else of lower magnitude is tit for tat.

Iranian proxies are not directly controlled by Iran. The Houthis may well be "doing their own thing". In any case, that is how Iran plays it. They can't control their proxy. Similar, from the Iranian point of view, Israel is a US proxy. Indeed, nobody can argue we control Israel's actions in Gaza. We have influence, but not control. Tit for tat.

Neither the US nor Iran actually want an armed conflict between each other. Both sides have real good reasons to avoid such an outcome. So far, this has resulted in both sides responding in a measured way to "obvious provocations". Direct attacks on each other's soil makes war unavoidable (IMO). Anything less is going to be "managed" by both sides. If, for example, a US warship is actually hit by a missile, that will mandate a serious response by the US. If that response is against Iran, not the Houthis, that will probably start a war. IMO, that could happen.

I think your last paragraph is important to consider. Lots of non state actors involved here who could really cause things to go to the next stage. If Iran had control of its non state actors I would feel much better.  
Another possible problem is that we can only hit the non state actors so hard.  I don't think we want to start another ground operation in Yemen, Syria, or Lebanon but if as you say they hit a Navy ship and do major damage with resulting casualties, direct strikes against Iran would probably result.  I am not a big fan of making a statement as to what we will not do, because if the event is catastrophic we would probably do what we said we wouldn't do. The whole thing makes me wonder if peace as we have known it will ever be possible in that part of the world. Should it ever appear that peace might happen, all one of the non state actors has to do is make a major attack on Israel and they would probably repeat what is now happening.

[GK3]

Similarly, Iran so far has been able to do whatever it wants through it's proxy forces in much of the middle east. Eventually, they will go "too far" and either Israel or the US will take military action. We need a way to let Iran know this can't go on. We don't have that AFAIK. That is the danger. Starting a war and occupying Iran is possible. Then what?

If the deaths of American military personnel isn't "too far", and the ongoing attacks by Houthis and others isn't "too far", then...what would constitute "too far"?

I obviously don't know exactly what constitutes a "red line" for the administration, but I think the correlation of forces is something like the following: The Iranians will respond to any killing of ethnic Iranian forces (e.g. the Quds force) in other countries (Iraq, Syria, Jordan, Lebanon, etc.) with like actions in the same area. The US does the same. That means that both Iranian and US personnel die in the middle east and no war is declared as a result. If the US attacks the territory of Iran, that will start a war. If a terrorist attack happens on US soil that can be traced to Iran, IMO that will result in the US striking Iran heavily and that will start a war. Anything else of lower magnitude is tit for tat.

Iranian proxies are not directly controlled by Iran. The Houthis may well be "doing their own thing". In any case, that is how Iran plays it. They can't control their proxy. Similar, from the Iranian point of view, Israel is a US proxy. Indeed, nobody can argue we control Israel's actions in Gaza. We have influence, but not control. Tit for tat.

Neither the US nor Iran actually want an armed conflict between each other. Both sides have real good reasons to avoid such an outcome. So far, this has resulted in both sides responding in a measured way to "obvious provocations". Direct attacks on each other's soil makes war unavoidable (IMO). Anything less is going to be "managed" by both sides. If, for example, a US warship is actually hit by a missile, that will mandate a serious response by the US. If that response is against Iran, not the Houthis, that will probably start a war. IMO, that could happen.

I think your last paragraph is important to consider. Lots of non state actors involved here who could really cause things to go to the next stage. If Iran had control of its non state actors I would feel much better.  
Another possible problem is that we can only hit the non state actors so hard.  I don't think we want to start another ground operation in Yemen, Syria, or Lebanon but if as you say they hit a Navy ship and do major damage with resulting casualties, direct strikes against Iran would probably result.  I am not a big fan of making a statement as to what we will not do, because if the event is catastrophic we would probably do what we said we wouldn't do. The whole thing makes me wonder if peace as we have known it will ever be possible in that part of the world. Should it ever appear that peace might happen, all one of the non state actors has to do is make a major attack on Israel and they would probably repeat what is now happening.