On his way to clinching the Republican presidential nomination, former Massachusetts governor Mitt Romney now faces a critical question: who will he pick as his running mate?

Or more precisely, what kind of person? With his struggle in the primaries to win voters who identify themselves as very conservative, members of the Tea Party or evangelical Christians, Romney will face pressure from the party’s base to pick a well-known conservative. But at the same time, the former governor, looking to defeat the first black president, also must consider another dynamic: in an increasingly diverse America, can he afford to run an all-white male ticket?

There is no specific evidence that voters are necessarily looking for, or expect, a minority or a woman on the GOP ticket. At the time, a sense of making history helped inspire voters, particularly the young and African-Americans, to campaign aggressively on Barack Obama’s behalf in 2008 and turn out in record numbers on Election Day. Republicans initially displayed similar enthusiasm around Sarah Palin, who would have been the first female vice-president, until a series of interviews suggested she was unqualified for the office.

Republicans have also sought to elevate figures like Florida Sen. Marco Rubio and Rep. Tim Scott (R-S.C.) in part to illustrate they are not out of step with the times.

But the challenge for Romney is similar to what John McCain faced in 2008: is there a minority or a woman who would both help the ticket win and is ready for the glare and media attention of being vice-president, as well as the intense scrutiny on their knowledge of policy issues? Rubio, while perhaps an asset in Florida because of his Cuban heritage, is only in his second year as a senator, as is New Hampshire’s Kelly Ayotte. Susana Martinez, the Mexican-American governor of New Mexico, is also in her second year in office.

All three have the potential to help Romney win a key swing state; they could also raise questions about their preparedness to assume the presidency if necessary, as Palin did four years ago.

Louisiana Gov. Bobby Jindal is a more seasoned politician, but gave a widely-panned speech in 2009, as the Republican tapped to give the response to President Obama. And as an Indian-American (a relative small minority group in America), ironclad conservative and governor of a state Romney will almost certainly win anyway, it’s not clear how Jindal would directly help the ticket on Election Day.

In terms of simply winning the election, Romney must make gains in at least one of the four segments of the electorate President Obama dominated in 2008: blacks, independents, Latinos, and voters between the ages of 18 and 29. He needs to win in traditional swing states such as Ohio and Iowa, by wooing white independents who backed Obama in 2008, as well as places like Colorado, North Carolina, and Virginia, where Obama benefited from stronger turnout among black and Latino voters.

Appeasing conservatives aside, there is little evidence Romney needs to pick someone like his top rival in the primaries, former Pennsylvania senator Rick Santorum, who has emerged as the favorite of conservative Christians and Tea Party members. Polls suggest most conservative voters dislike President Obama strongly and will quickly shift to Romney in the general election.

At the same time, Romney likely can’t afford to lose votes in the party’s base by picking a running mate who supports abortion rights, such as former Secretary of State Condoleezza Rice or Maine Sen. Susan Collins.

Those dynamics suggest Rubio, despite his repeated claims that he won’t be on ticket, is almost certain to be strongly considered. He is beloved by Tea Party Republicans, could help win Florida, may appeal to Latinos nationwide, and Republicans could cast the 40-year-old as part of a new generation of politicians who can appeal to young voters.

At the same time, a series of controversies around Rubio, mostly notably about whether his parents were truly exiles of Cuba after Fidel Castro gained power there or came to the U.S. before Casto’s regime, could give Romney pause.

Another strong potential candidate for Romney could be Bob McConnell, who would not bring diversity, but is the governor of a key swing state (Virginia) and has the executive experience Romney has been touting in himself.

Four years from now, when Ayotte, Martinez and Rubio are more seasoned politicians, it’s hard to imagine the GOP will have this problem at all. In fact, if Romney opts against picking a woman or a minority in 2012, he may be part of the last ticket of either party that doesn’t include a woman or a minority. The demographic shifts in the country raise the possibility that any future presidential ticket must include ethnic or gender diversity.

Follow Perry Bacon Jr. on Twitter at @perrybaconjr