This was obviously just a stray threat that hit Cantor randomly, probably meant for someone else.
We're all having a good time ridiculing the commie dopes, but if you remember back, they actually did the same thing when a nutcase got all the way into Tom Delay's office in the Capitol and shot two policemen on the way in. IIRC one of those cops INSIDE TOM DELAY'S OFFICE killed or seriously injured the perp--enough to stop him.
Then the idiots put out a news story that the perp was probably REALLY after Gephardt. It was obvious that that was true too. After all, there was a stairway near Delay's office that led to Gephardt's office which was on a different floor...