Trump declares national emergency to protect US networks
techcrunch.com
techcrunch.com
Also, the president does not have the authority to start a war; that is delagated to congress. Of course, by that standard the US hasn't had a war since WWII.
There’s a lot to unpack there, from congressional abdication of their responsibility of oversight to the changing nature of warfare.
But I would note that congress hasn’t entirely abdicated its oversight role in declaring war, modern congresses pass an “Authorization for Use of Military Force”, or the AUMF as it’s called, to find and detail their approval for military action.