The current administration sees China as a huge threat, the previous several administrations (republican and democrat) did not. Or if they did, they thought the way to deal with the threat was through economic cooperation.
China has been a threat to US interests in the Pacific for decades. Now China is the regional hegemonic power which dwarfs the weak US Pacific partnership. China's international influence will continue to grow and they will likely achieve their 100 year plan. That's not really fearmongering, China has plenty of problems but they will eventually succeed.
Because in 5G it is demonstrably ahead technically and for the first time holds a significant number of patents. This is considered a "national security concern" because well, you know, if America isn't number one (USA! USA!) it is obviously because somebody else cheated, and America not being number one is obviously equivalent to the end of the world. /s
