Re: What was good enough for Challenger...
"There's nothing in there where he says they should deliberately risk lives with an unproven launch platform just to meet an arbitrary timeline."
That's because the article left a sentence out. He's committing to making EM-2 launch on SLS. EM-2 is still slated to be a crewed flight. So the very first launch of SLS is now scheduled to carry humans. They're requiring the SpaceX have 7 flights on the block 5. Even if EM-1 was on SLS, EM-2 falls on the second mission. 2 and 1 are both less than 7.