Why? Prior to August 1990 Saddam's Iraq was regarded as a very useful counterweight to the Ayatollahs' Iran which had been regarded as the real threat by the US since the 1979 Iranian Revolution. If anything the US might have aided Iraq through money and arms in order to prevent Iranian expansion.
Might have? This is exactly what the US had been doing before 1990!
To be sure, with the Iranian capitulation ending the long Iraq-Iran war, US support was cooling down, which possibly has some bearing on why he did choose to invade Kuwait OTL.
I'm aware of two factors that probably motivated him most:
1) Kuwait had loaned Iraq a whole lot of money during the I-I war, and now that it was settled adversely from the Iranian POV, the monarchy was calling in the debt. Saddam asked them to forbear it or anyway go slow with payment demands since Iraq was also battered and I daresay the slack state of the global economy did not help either. But they wanted their debt repayed promptly. From SH's point of view, Iraq had fought and bled to secure the interests of all the Gulf states and principalities, now they, having sat back and risked nothing but money, wanted the money back too.
2) The Iraqis accused Kuwait of offset oil drilling, with wells on the Kuwait side of the border slanting across into fields under Iraq. I suspect this was the truth. In the context of Kuwaiti insistence on strict repayment of debts, this sort of thing would be all the more infuriating.
Although I guess American aid had slowed down to a trickle compared to wartime support the Yankees had given, the Bush administration still professed to support SH; this did not change until the invasion. Had he swallowed his pride and anger and avoided doing anything so drastic (which might have been too much to ask of the thug) I'd think the US would have regarded him as an asset from that day to this, at least as long as Iran was seen as posing any sort of potential threat.
He'd also be seen as a bulwark against other brands of Islamic fundamentalism, as others have suggested or implied above.
Whether it would have been possible to engineer sufficient war fever to take on as misguided an adventure as a US invasion of Iran is really hard for me to judge, gobstopped as I am by some of the incredibly foolhardy things we've done in the OTL interim. I rather hope not and I don't think the Iranians would have done anything worse than OTL to serve as provocations, no matter how energetically spun the OTL issues might have been by US hawks.