Seriously? Trump could have done this almost 3 years ago?
And Obama could have done it 8 years ago and Bush could have done it 15 years ago. What's your point? The article says his predecessors thought of doing it but held back.
The massacre of the American family, LeBaron, in Northern Mexico has turned new attention to the problem let alone, this whole political border-wall/border enforcement battle that is going on.
What would the designation mean?
When a group is designated as a terrorist organisation in the US, it becomes illegal for people in the US to to knowingly offer support.
Its members are also banned from entering the US. If they are already in the US, they face being deported.
If financial institutions discover they have funds connected to the group, they are required to block the money and alert the US Treasury Department.
https://www.bbc.com/news/world-us-canada-50568812
This is actually likely, a long-time coming and it surely is no easy decision to make. As I said, potentially, we could see some blowback.
With all due respect, to say "why didn't he do this three years ago" sounds like one is not up on the news.