How was the iran contra scandal a threat to american success?

The Iran-Contra affair was a scandal involving the US and Iran. Iran was at an arms embargo at the time, so no arms were supposed to be sold to this country. The US though was secretly selling arms to Iran. This came out on the surface and became a big scandal. The US administration was trying to justify this move that they have done it order to free American hostages held in Lebanon by Hezbollah, but it turned out that the arms sale started much earlier then that. Apart from having a badly damaged reputation, both at home and on the international scene, the US success in the region was also damaged. The Arab world was a sworn enemy of Iran, and they thought that the US is their friend and protector, but it came on surface that the US is arming their enemy, so it disrupted the relations with these countries for the time being.