Ted Cruz surprised many election pundits by forcing a July 31 runoff with Lt. Gov. David Dewhurst for the Republican senatorial nomination. Cruz, however, trailed the lieutenant governor by 144,422 votes in Tuesday’s ballot tally. How does Cruz, who was been out spent by Dewhurst 5 to 1, mount an successful runoff campaign?

Partisan primary runoff elections are largely determined by which candidate is able to turnout more of their general election supporters. On average, 70%-75% of general election primary voters return for the runoff. For Cruz to overtake Dewhurst, he would have to return almost 94% of his general primary vote, holding Dewhurst to just a 72% turnout among his general election supporters. The likelihood of this large difference in turnout between the candidates’ supporters seems remote. Failing to gain a significant turnout advantage over Dewhurst, Cruz might turn to wooing support from voters of other primary candidates, most notably the 185,934 supporters of former Dallas Mayor Tom Leppert. An endorsement from the Leppert would go a long way to achieving this goal, but the primary campaign does not suggest a Leppert endorsement of Cruz is likely. It seems unlikely that more than half of the Leppert’s general election voters would return for the July 31 runoff. Pre-primary polls further suggest that a majority of Leppert’s supporters would choose Dewhurst over Cruz in a runoff. Finally, failing to win the turnout battle or bringing Leppert supporters and other primary voters to his camp, Cruz must rely on his opponent to make a mistake. Cruz’s election night challenge to Dewhurst to participate in five election debates is an attempt to create a setting in which Dewhurst might make a “Perry-like” misstep which Cruz would then use to peel away supporters of Dewhurst to his candidacy. For such a strategy to work, Cruz needs Dewhurst to make a misstatement(s) in a debate or on the campaign trail and for Cruz to have the money to publicize the faux pas. The latter seems likely, given promises from national conservative groups to fund Cruz’s runoff campaign. It is not, however, likely that Dewhurst will either debate Cruz or, if he does, make “Perry-like” misstatement(s).

Final assessment: A Dewhurst victory in the July 31 runoff election is far from certain, but it is more likely than a Cruz victory, barring one or any of above occurring.

Robert Stein, Ph.D., is the fellow in urban politics at the James A. Baker III Institute for Public Policy. He is also Rice University’s Lena Gohlman Fox Professor of Political Science and a nationally recognized political analyst and expert on elections.