We have to assume that the Trump administration is preparing to attack North Korea and/or Iran, and we need to put every possible roadblock in their path. People from diverse political and moral schools of thought recognize that what they intend to do is illegal, immoral, and pretty much insane.
Now we need to raise the alarm, and organize a response.
I've found the following groups to be speaking out against preventive wars:
1. Buchanan conservatives (The American Conservative)
2. Catholics academics (Unclear about the conference of bishops, but they likely would come out against invasions)
3. Libertarians (Ron Paul, Rand Paul?)
4. Your standard anti-war, anti-state leftists.
We Will Breathe the Ashes of the Dead for the Rest of Our Lives