The men are so near to each other in all their convictions and theories of life that nothing is left to them but personal competition for the doing of the thing that is to be done. It is the same in religion.

The apostle of Christianity and the infidel can meet without a chance of a quarrel; but it is never safe to bring together two men who differ about a saint or a surplice.

— Anthony Trollope, “Phineas Redux”

HOUSTON -- The average high temperature in Texas on July 31 is 94 degrees, which might matter in the selection of this state's next U.S. senator. Or perhaps the crucial fact will be a residue of Reconstruction.

With Sen. Kay Bailey Hutchison having decided not to seek a fourth full term, a May 29 primary winnowed a field of nine competitors for the Republican nomination — and, effectively, for the seat from this crimson state — to two men who are very near to each other in all their convictions and theories of life.

David Dewhurst, 66, got rich in the oil and gas business, which is neither a nest of liberals nor resented by Texans, and for nine years he has been lieutenant governor, which in Texas is an approximation of Caesar. He says that during Reconstruction the federal government imposed carpetbagger governors, so in 1876 Texans wrote a constitution that made their governor the nation's weakest and made a muscular lieutenant governor. He appoints all chairmen and members of the state Senate committees, who serve at his pleasure; he schedules all legislation; no senator can speak without his recognition.

The Ted Cruz campaign says dependency explains why 18 of 19 state Senate Republicans recently signed a letter in support of Dewhurst, who must worry that Tea Party members and other conservatives look askance at persons who play too well with others. Cruz has degrees from Princeton and Harvard Law School. Dewhurst, who played basketball for the University of Arizona, is in the Texas Rodeo Cowboy Hall of Fame. Advantage Dewhurst.

Each candidate has endorsements from national conservative luminaries. Cruz, however, has the cachet of someone fluent in the vocabulary of intellectual and constitutional conservatism, and has none of the ideological impurities that result from leading legislative coalitions. Advantage Cruz.

On 99 percent of U.S. Senate business, Cruz and Dewhurst probably would vote alike. Yet the ultimate Republican epithet, the M-word — “moderate” — has been bandied. Cruz supporters say Dewhurst is one, which is nonsense. Dewhurst rides roping horses that can go from a standing start to 40 miles per hour in two strides, which is about how fast he recites this catechism: Texas is “the most conservative, most pro-growth, most pro-jobs, most pro-life state in the country” and would not tolerate a moderate lieutenant governor. He says he has presided over 51 tax cuts and has slashed $14 billion from the state budget while Congress has been unable to cut $23 billion from a budget 41 times bigger.

Dewhurst counters the M-word accusation by going nuclear. He notes darkly that Cruz is an eloquent speaker and a Harvard lawyer just like you know who. Dewhurst's long legislative career presents Cruz — as Mitt Romney's business career presents Barack Obama — with opportunities for histrionic (and synthetic) indignation about this or that vote or compromise. But, then, Cruz's record as a lawyer has left him vulnerable to similar rhetoric from Dewhurst's campaign about some Cruz clients who were unsavory (a “judge-bribing felon”) or impolitic (a Chinese tire company).

If Dewhurst wins, Capitol Hill gets a veteran conservative legislator. If Cruz wins, congressional conservatism's small, but valuable Doesn't-Play-Well-With-Others Caucus adds a member.

If Dewhurst had won five and a half points more in the primary, he would have had 50 percent and the nomination. The primary should have been in March, but judicial wrangling about redistricting disrupted the political calendar, and Texas has no experience with an important election, such as this runoff, in late July. There might be as much as a 50 percent decline from the 1.4 million who voted May 29.

The Cruz campaign believes, plausibly, that the high-octane ideology that fuels his Tea Party and other supporters, including many of Texan Ron Paul's, will power them to the polls come Hell or high temperatures. It is unclear whether it speaks well of them that they, like Noël Coward's mad dogs and Englishmen, will go out in the midday sun, even to vote in what resembles a dispute about a saint or a surplice.

George Will's email is georgewill@washpost.com.