Check out this article. There has been strong evidence that there are connections between Al-Qaeda and Iran & their proxies for nearly 30 years. This information comes directly from the 9/11 commission report, State Department reports, and the Obama administration. Obama used the 2001 AUOMF resolution as justification to attack ISIS without congressional approval. I have to assume that Trump could do the same thing with Iran if he chose to.
https://www.vox.com/2019/6/14/18678809/usa-iran-war-aumf-911-trump-pompeo
In late 1991 or 1992, discussions in Sudan between al Qaeda and Iranian operatives led to an informal agreement to cooperate in providing support — even if only training — for actions carried out primarily against Israel and the United States.
Iran’s proxy group in Lebanon, Hezbollah, also helped train al-Qaeda operatives ahead of its 1998 bombings of US embassies in Kenya and Tanzania. In 2003, al-Qaeda killed more than 30 people in Saudi Arabia’s capital, Riyadh, and the plotters fled to Iran. Eight years later, the Obama administration said there was a "secret deal" between Iran and al-Qaeda “to funnel funds and operatives through its territory.”
From a 2012 State Department report: Iran “allowed AQ [al-Qaeda] members to operate a core facilitation pipeline through Iranian territory, enabling AQ to carry funds and move facilitators and operatives to South Asia and elsewhere.”
eh....that's pretty thin, but we've gone to war over less