Here's some context for you C2:
McCain isn't a fan of F-35 for a number of reasons, mostly political.
His State is Arizona.
Arizona (Davis-Monthan) has a huge A-10 community and trains A-10 pilots.
Congressmen need votes and need to represent their communities.
A-10 pilots, like Vermont ANG F-16 pilots, don't want to lose their jet.
You join the dots. Oh, and you're right, the F-35A isn't IOC yet. That happens later this year after the USAF puts it through its paces in the missions it wants it to prioritise amongst the wider fleet.
Sounds like Gen Welsh wants to keep A-10 but doesn't have the resources to do so. That's actually the issue at play here.