Following on from looking at who will be running for the Democrats in four years time, these are some of the likely Republican contenders in the event of a Romney loss. If he does lose this year, it is highly improbable that he'll run again. Taking into account his previous attempt for the nomination, he has been in the process of running for president for seven years. After being rejected by his party and then by the nation, he might start forming the idea that Americans might not want him in the White House.
In the wake of a Republican defeat, it will leave the party with questions over how it once again makes itself an attractive proposition to American voters. Over the past four years, it has moved to the right. Will it move further onwards or return to the centre to capture those who are mistrustful of Obama's spending plans yet dissuaded by the party's rhetoric on social issues?
If it is to go for the centre, then its image of being a party for old white men will have to change. Changing population demographics mean that the party will have to field candidates that appeal to non-caucasian groups. Fortunately for them, there is a new generation of Republicans who fit this description.
Marco Rubio
The son of Cuban immigrants, Rubio has what very few Republican candidates have; an authentic connection to the Hispanic population. Whilst George W. Bush and Mitt Romney have recorded campaign ads in Spanish, Rubio is from Spanish-speaking stock as well as being an immigrant success story. His experiences as a second generation Cuban-American are something that he will resonate with many of the new voters in the south. He was one of the people vetted for Romney's running mate before the call went for Ryan.
Why he will run
Rubio has been a popular senator of Florida and given the importance of the state in the electoral college, he has a firm base upon which to make a run for president. He is different from other Republican candidates given his heritage and showing that you can be born to immigrant parents and still be a Republican.
Why he won't run
The only thing stopping a Rubio run in 2016 is a Romney win this year. It is highly likely that he will keep his place in the Senate in 2014. Such is the esteem in which he is held within the party that he was the person chosen to introduce Mitt Romney at the Republican National Convention. Only something scandalous or catastrophic can stop him in the event that Romney loses.
Bobby Jindal
Piyush 'Bobby' Jindal came within six months of not being able to run for president, his parents only arriving in the country half a year before his birth. Since then, Jindal has become a leading light in the party, another of the new generation of Republicans whose parents are immigrants. A popular governor of Louisiana, he was courted by John McCain as a potential Vice President in 2008 before he went for Sarah Palin.
Why he will run
Like Rubio, Jindal may feel that he can offer something lacking in recent Republican candidates; youth and racial diversity. He is also attractive to Republican voters due to his 100% pro-life voting record and opposition to same-sex marriage.
Why he won't run
When given the chance to make an impression on the national stage, he has failed to deliver. A planned speech at the 2008 Republican National Convention was disrupted by Jindal going back to Louisiana to assist in the preparations for Hurricaine Gustav. Then he was given the opportunity to respond to President Obama's first speech to Congress. His response, which referenced the ineffective response to Hurricaine Katrina and argued against government intervention, was savaged by both parties and their supporters. Seven years down the line and Jindal might not have enough support within the party to make a viable run.
Nikki Haley
Like Jindal, Haley was born to Indian parents who immigrated to America, and like Jindal, she is the governor of a southern state. Her win in South Carolina was enabled by endorsements from Mitt Romney and Sarah Palin. She is a member of the Tea Party and has held a consistent conservative stance on such issues as abortion, taxation and immigration.
Why she will run
Given that she gained the endorsement of both Mitt Romney and Sarah Palin, it is clear that she has popular support within the party. Her membership of the Tea Party may be a help or hindrance depending on whether the economy keeps stagnating and the direction taken by the Republican Party.
Why she will not run
Although an Indian-American female Republican candidate would be a first, it doesn't necessarily mean that Haley would be a standout from the field. Her views match those of many conservative voters but she does not have enough of a national profile to have a realistic chance yet. Perhaps 2020 will be her year.
Scott Walker
Wisconsin Governor Scott Walker is much more of an orthodox Republican candidate. He became governor of the state two years ago and survived a recall election the following year. His politics are in tune with many Republican voters with a consistent conservative voting record on abortion, taxes and same-sex marriage.
Why he will run
Walker will feel that his voting record and political stance will make him an attractive candidate within the party. Taking on the unions in Wisconsin and triumphing will have done his chances no harm at all.
Why he won't run
Walker does not enjoy a great deal of popularity in his own state. The recall shows that he is a divisive figure within the state and his victory in that election was not by a big margin. Lacking momentum within his own state could be a problem further down the line.
Chris Christie
The charismatic governor of New Jersey ummed and ahhed about standing this year before deciding against it. His keynote speech at the Republican National Convention made quite an impression and propelled him onto the national stage. He will chair the Republican Governors Association in 2014, which is viewed as a springboard to a future presidential run. The position gives him access to a multitude of senior Republican figures and potential donors.
Why he will run
He has put everything in place for a run in 2016: a successful term as governor, which saw him taking on the unions and opposing same-sex marriage. Allied with this is his popularity within the party and his time spent as the chair of the Republican Governors Association.
Why he won't run
Other than a Romney win, the only thing that stands between Christie and a run in 2016 is the gubernatorial election next year. In the same way that it is vital for Cory Booker, lose this and all this momentum will be derailed.
Other candidates: Rand Paul, Jeb Bush, Paul Ryan