That didn't happen when just 1 Senator went and didn't live stream his visit. If they really wanted to, they could have claimed he did something violent or something. There'd have been no way to prove otherwise. And he was able to get them to crack just by holding a press conference. The bad PR from 1 guy getting denied scared them so much that they let him meet Abrego Garcia.
So why do you think they'd do that if there was a large group and the entire thing was being live streamed?
First, I said Representatives and Senators. There are 260 Democrats in Congress (well, 258 +2 independent who caucus with Dems), not 45. But that's beside the point. What are they doing for us in Congress right now? Absolutely nothing. Hell, a bunch of Dem Senators are acting like Vichy collaborationists helping the fascists confirm appointments and pass their CR. They're actively working against us by just sitting in Congress.
But even that's beside the point. They're not going to arrest or kill a bunch of sitting US members of Congress. Even just saying 'no' to 1 of them was such a bad look that they completely folded and, for the fist time ever, let someone out of CECOT, even just temporarily. They've NEVER let anyone out before, and Van Hollen just showing up on his own scared them enough to crack.
Why do you think an even greater number would scare them less?