the US might need to return again and again

War isn't just great for Islamic radicals, it's also in the interest of hedge funds and military contractors.

I suspect this is why the person leading the attack on the Iran deal, Lindsey Graham, is bankrolled by them.

Here's what's in it for energy companies

 One particularly salient opportunity is for Iran to develop its huge natural gas resources to become a major supplier to energy-starved European Union (EU) countries as well as its immediate neighbors in the Middle East. Beyond allowing Iran to advance its goal of being a central figure in the Middle East economy, these developments would help insulate it from further U.S. economic or military attack.

 Much like ISIS, a forever war doesn't sound too bad to US mercenaries either. War with Iran would be the goose that laid the golden egg.
 
Via Zack Beuchamp's article on Vox:

If the first round of strikes didn't destroy every target, the US might need to return again and again. It would require the US to "continue a sustained campaign over a period of time and re-strike after an initial battle damage assessment [if] it is found that further strike sorties are required," defense analysts Anthony Cordesman and Abdullah Toukan write in a comprehensive 2012 Center for Strategic and International Studies report.

It should be noted that the main reason Israel opposes this deal harmonizes with the above contractors, but is deeper than that. Israel does not believe it can win through diplomacy, so it must unilaterally oppose it, without revealing that is the principle. Via Document 93B (PDF):

[Henry] Kissinger: "[...] Diplomatically you have not won the war. You have won it tactically.
[Israeli Prime Minister Golda] Meir: Diplomatically we will never win.
Kissinger: Exactly. That is the tragedy.