WASHINGTON -- "Do you think he'd do it?" That was the first question Ronald Reagan asked when, 24 days before the 1976 Republican convention, his campaign manager suggested that Reagan immediately name Pennsylvania's Sen. Richard Schweiker as his running mate. Reagan was narrowly behind in the delegate count as he attempted to wrest the nomination from President Gerald Ford. Three days later Schweiker joined the ticket.

This was designed to pry loose some Ford delegates, particularly among the 103 of Pennsylvania's delegation (Schweiker was one of them), and prevent Ford from clinching the nomination before the Kansas City convention.

A callow young columnist without a lick of sense (George F. Will) criticized the tactic as "slapstick," but it worked: Walter Cronkite pulled back what would have been that night's CBS lead story saying Ford's nomination was assured, and the battle raged until the convention.

Today, Hillary Clinton in extremis could contemplate a similar maneuver: Pennsylvania's April 22 primary may be climactic and Gov. Ed Rendell is available. But so far only John McCain is certain to need a running mate, and his choices are limited by his needs and his nature.

McCain needs someone who will help him win and be a plausible president during the next four years. He has been in Washington more years than Clinton and Barack Obama combined, and today, as usual, but even more so, Washington is considered iniquitous, partly because McCain, our national scold, incessantly tells the country that its capital is awash in "corruption."

It would be reassuring were he to select a running mate with executive experience administering something larger than a senator's office. So an otherwise well-qualified senator, such as Kay Bailey Hutchison, might not be suitable.

Besides, McCain, who will be 72 on Inauguration Day, might need someone younger. Which would prevent the selection of Colin Powell, 70. Also, a McCain-Powell ticket would slight domestic issues, with which Powell has never been professionally engaged and McCain has rarely been preoccupied.

In politics, gratitude is optional but admirable, and McCain is indebted to Florida Gov. Charlie Crist, 51, who endorsed McCain on the eve of his state's primary. Because the disastrous recent performance of Ohio's Republican Party will make it difficult for McCain to hold that state's 20 electoral votes that Bush won, McCain must keep Florida's 27. Crist won the 2006 Republican gubernatorial primary 64-33 even though, as Michael Barone writes in his Almanac of American Politics, that election was notably unpleasant: "Here a candidate was attacked for being both gay and for fathering a child out of wedlock."

Crist remains popular, but not more so than his predecessor, Jeb Bush, 55. Bush, however, seems determined to take a sabbatical from politics. And it might seem tribal to have a Bush on the national ballot for a seventh time in eight elections.

Three two-term governors might help McCain, including Mississippi's Haley Barbour, 60. He has two things McCain lacks -- impeccable conservative credentials and a genial disposition. He was conspicuously competent in Katrina's aftermath. As a political director in the Reagan White House, and as national party chairman, 1993-1997, when Republicans ended 40 years of Democratic control of the House of Representatives, Barbour demonstrated political subtlety and an agreeable absence of righteousness, qualities McCain as president would need close at hand. Unfortunately, Barbour also was a lobbyist for a while, and the right to "petition the government for a redress of grievances" is another part of the First Amendment that the co-author of McCain-Feingold finds unimpressive.

South Carolina's Gov. Mark Sanford, 47, is more of a maverick than McCain, and Sanford faults his state party for being insufficiently conservative. His frugality has had him at daggers drawn with the state Legislature, which Republicans control. His populism is an acquired taste -- he should not have lugged those two live pigs into the Legislature to express his disapproval of pork -- but he favors expanding school choice, eliminating the state income tax and, at the national level, reforming entitlement.

Finally, Minnesota's Tim Pawlenty, 47, is national co-chairman of McCain's campaign. His is the only state (10 electoral votes) to go Democratic in the last eight presidential elections. The candidate who wins a majority of the electoral votes in the Mississippi Valley usually wins the White House. Pawlenty is a center-right politician in a center-right country, and the Minnesota Twins will open a new ballpark in 2010 because he helped to provide public funds, a practice that red-blooded Americans deplore in principle but enjoy in practice.