He did wangle an invitation. He did an end-run around the woman who is the President of the Pontifical Academy, in what she termed an act of monumental discourtesy, and secured an invite from a Bishop board member instead.
And the Pope himself said the 6 a.m. encounter was a handshake and nothing more.
http://www.cruxnow.com/church/2016/04/16/pope-francis-calls-sanders-greeting-only-common-courtesy/
On the Vermont senator, Francis said he greeted Sanders on Saturday morning as he was leaving the Santa Marta, the hotel within Vatican grounds where the pope lives.
Sanders was staying at the same residence, because thats where all participants in the Vatican conference he attended on Friday were spending the night. The only exceptions were Presidents Evo Morales of Bolivia and Rafael Correa of Ecuador, who stayed at their countrys embassy in Rome.
This morning as I was leaving, Senator Sanders was there, Francis said. He knew I was coming out at that time, and he had the kindness to greet me.
When I came down, he introduced himself, I greeted him with a handshake, and nothing more, the pope added. Its common courtesy, this is called common courtesy.
If someone thinks that greeting someone is getting involved in politics, he said, I recommend that they find a psychiatrist.
http://www.bloomberg.com/politics/articles/2016-04-08/sanders-accused-of-discourtesy-in-seeking-vatican-invitation
Democratic presidential candidate Bernie Sanders plan to attend a Vatican-sponsored conference put him in the middle of a diplomatic row as a senior Vatican official accused the senator of showing monumental discourtesy in angling for an invitation that puts a political cast on the gathering.
Sanders made the first move two or three days ago, Archer said. She did not know whom he or his representatives contacted. His use of it is clearly a pretext, she said. There are just 20 academics and there will be nothing of policy relevance.
However Bishop Marcelo Sanchez Sorondo, the chancellor of the Academy, speaking on the phone from New York, said he extended the invitation to Sanders, though he repeatedly declined to say who initiated the contact.