Huawei isn’t a threat to national security. Consumer computer software is not a threat to national security. This is a justification for a trade war the president and his advisors want to engage in.
Turns out that if you can compromise someone's phone, you have a window into everything that person does, sees, and hears; both online and off.
And other countries have security concerns with Huawei besides US so this isn't just about the trade war.