noun. A joint sponsor

verb. To sponsor jointly with another

verb. sponsor together with another sponsor

"In light of the way you cleverly parse other parts of your response "it COULD result in", "especially in regions where," etc. (emphasis mine), it's obvious that you are aware that the implication of calling someone a "cosponsor" of a piece of Senate legislation implies the joint cosponsor whose name is on the bill."

patronise  patronize  sponsor  

cosponsored  cosponsoring  cosponsors