The articles I’ve read suggest they’ll purchase the company for approx $14 billion and have promised to invest an additional $14 billion in the USA (see link below).
It’s the additional $14 billion investment that the Senator is trumpeting.
apple.news
Trump warms to Nippon Steel, backing ‘partnership’ with US Steel — The Guardian
Biden had blocked Japanese acquisition, citing national security, with Trump previously agreeing he was ‘totally against’ it