The former New Mexico governor is positioned to build on what Rep. Ron Paul tapped into in 2008. Johnson believes in less spending, lower taxes, and a noninterventionist foreign policy. As governor, he vetoed 750 bills, a total that at the time was more than that of the other 49 governors in the U.S. combined. An early opponent of the Iraq War, Johnson has been vocal about his opposition to President Obama's surge of troops in Afghanistan, saying it will cost more American lives and not solve the terrorist threat.
Con: Johnson's outspoken support for legalizing marijuana may help him raise money among advocates of that position but it could also limit his support among Republicans who might otherwise be drawn to other parts of his small-government agenda. Johnson may also be hampered in the GOP primaries by his support for abortion rights.
The former senator from Pennsylvania recently told ABC News' "Top Line" Webcast that he is "absolutely taking a look
" at running for president in 2012. A staunch foe of abortion rights, same-sex marriage and illegal immigration, Santorum could appeal to some of the socially conservative voters who participate in the Iowa caucuses. As part of his exploration of a presidential run, Santorum has traveled to Iowa and South Carolina.
Con: Santorum's biggest weakness is that it is hard to make the case that you should be your party's presidential nominee when you were defeated in your most recent bid for re-election to statewide office. And yet that is exactly the situation that Santorum finds himself in: The Pennsylvania Republican was defeated in 2006 by Democrat Bob Casey. Santorum has also been criticized by Mark McKinnon, a former Bush and McCain adviser, as being "dangerous" for the future of a GOP that needs to attract Latinos.
The former New York governor has not received much attention, but there are several signs that his is interested in making a run for the White House in 2012. Top GOP donors have asked him to run against Sen. Kirsten Gillibrand, D-N.Y., but he has told them that he does not want to enter the race because he has his eye on the White House. Pataki dipped his toes
in the presidential waters by traveling to Iowa last year, the state that hosts the first presidential nominating contest. In February, he is planning to visit New Hampshire, home of the first presidential primary.
Con: Pataki actively flirted with running for president in 2008 but ultimately passed on the race. Many of the questions which were raised then are still relevant now: How does a Republican who supports abortion rights and gun control win the nomination of a party that has become increasingly conservative?
ABC News' Matt Loffman contributed to this report.