Tea-Party Favorite Surges in Texas Senate Race

By NATHAN KOPPEL

AUSTIN, Texas—Tea-party favorite Rafael "Ted" Cruz is aiming to pull off an upset in a U.S. Senate primary runoff next week, aided by a rush of super PAC spending.

Just weeks ago, Texas Lt. Gov. David Dewhurst appeared to have a comfortable lead in the race to become the Republican candidate—the main event in the conservative Lone Star State—after he finished first in the May primary. But his 10-point margin wasn't enough to avoid next Tuesday's runoff with Mr. Cruz, a former Texas solicitor general.

Now, against a backdrop of heavy spending by independent political-action committees, Mr. Dewhurst looks to be in the fight of his life. Recent polls suggest momentum has shifted to Mr. Cruz, a Harvard Law School graduate and son of Cuban immigrants....

"Without the outside money, Cruz would not be in the race," said Cal Jillson, a political-science professor at Southern Methodist University in Dallas who still predicts Mr. Dewhurst will eke out a win....