By now, Mr. Bush was cornered. He was surrounded by signs that said "Pittsburgh is a Santorum Free Zone," "Honk if you're sick of Rick," and a crowd growing increasingly louder, according to Mr. Vandenburgh.
"We don't want you here," protesters chanted.
Port Authority spokesman Bob Grove said six or seven officers responded to the scene to control the crowds.
He said Mr. Bush had been walking in the area near the T-station and the incident happened spontaneously when about 50 pickets "tailed him and stayed with him and went into the Wood Street station."
About 75 protesters remained on the street, said Mr. Grove.
He said the crowd was asked repeatedly to disperse.
Mr. Grove said a Port Authority canine unit was called in to help with crowd control. Two officers used their tasers to stun two protesters who "were asked to leave, but did not go," Mr. Grove said.
The tasers he said were empty of the cartridges that supply a more powerful charge.
"It was a very tense situation. They were very close to the governor and shouting on top of him."
As a precaution, the governor was ushered into a T-station supply closet and stayed there until the crowd left.