This is an example of what happens when trust, integrity and politics collide with an appropriate test of the Wireless Emergency Alert system (WEA). See this Huffington Post news item, New FEMA Alert System Would Have Trump Message You Directly. Here is a direct quote from someone when she read the above item, "What a dreadful idea. I automatically discount anything Trump says."
For the facts (not alternative facts), see this blog post of mine from earlier this week, National Wireless Emergency Alert (WEA) Test — September 20.
What really is at stake here is presidential credibility. Should we have a national crisis, and the President speaks to the nation via a WEA or an EAS alert or in an address to the nation from the Oval Office or a Joint Meeting to Congress, over half the nation is likely not to believe everything he has to say. This is a terrible situation to be in--when it comes to issuing an alert or rallying the nation for some specific purpose.
The closest I've seen the United States get to that point in my life time was the Cuban Missile Crisis and then President Kennedy addressing the nation. A majority of people thought we were on the brink of WWIII and a nuclear holocaust. I distinctly remember my basketball coach saying, "It looks like war."