There's an interesting article out there I read (if you need me to link it, I can go find it), that says that while it takes a 2/3 Senate vote to remove a sitting president, the Senate rules for their impeachment trial would be agreed to before the proceedings start, just like what the House did. Here's the catch, those rules for setting up the process only require a majority vote, not a 2/3 vote. So if 3 Republicans break ranks and force a SECRET impeachment vote (ie, their votes would not be a matter of public record), the chances of 20 Republicans voting for removal increases significantly.