Next week will see primaries in Arizona and Michigan on 28 February and the Washington caucuses on 3 March. The final debate before Super Tuesday on 6 March is tonight in Phoenix, Arizona, making it arguably the most important debate to date.
This week's campaigning may prove to be make-or-break for Mitt Romney. If he wins in Arizona and Michigan, he once again cements himself as the frontrunner in the GOP race. However, should Santorum take them then he will have lost more states than he has won and proven that he cannot connect with the conservative right.
The race remains volatile, with slim margins between Santorum and Romney in Arizona and Michigan. Although Romney is expected to win in Arizona -- laregly due to its significant Mormon population -- his position is precarious and will be undermined should Newt Gingrich's supporters switch their allegiance to Santorum and decide that he is now the only viable conservative alternative to Romney.
Mirroring John McCain in 2008, Romney also seems to have an edge with the Latino population in Arizona. Even if he loses the white vote to Santorum, a big win among the Latinos could still mean that Romney takes the state.
Crucially, Arizona is also a winner takes all state meaning that it gives all of its 29 delegates to the candidate with the most votes, regardless of how close the race is. Since Michigan is seen as more fertile ground for Santorum's message, it is unlikely that he will pour valuable resources into Arizona.
If polling predictions show Romney with a significant lead in Arizona, Santorum may well pull out in order to focus his efforts on Michigan.
Michigan, however, is a different story and may prove to be a turning point in deciding the Republican nomination. Despite the fact that Romney was born in Michigan, his father serving as governor there for six years, and has the endorsement of most Michigan GOP leaders including the governor, the more conservative and blue-collar electorate are likely to favour Santorum.
The Romney camp is spending more than twice as much as Santorum and his allies in Michigan. The Massachusetts governor ensured that he successfully dominated the airwaves in Florida and looks set to do the same in Michigan. He will also be helped by fellow candidate Ron Paul's recent ad attacking Rick Santorum as a faux fiscal conservative.
However, Michigan is an open primary, meaning that any registered voter can participate, making it difficult to predict the outcome. Non-Republicans will make up a third of the electorate and could be the determining factor. Should Democrats decide to vote and shake up the race - as they did in 2000 when they voted for John McCain over George W Bush supporter John Engler - it could be Santorum who leaves Michigan the victor.
Also making Michigan tough to predict is the fact that, like Florida, it is a very divided state. While the northwestern parts are more conservative and therefore more likely to vote for Santorum, the southeastern parts, including Detroit, are wealthier and likely to indentify more with Romney than evangelical Santorum.
A victory for Santorum in the Washington caucuses on 3 March would give the Senator some much needed delegates, although since the voting is after the Arizona and Michigan primaries, the outcome may be influenced by the results there.
With next week's primaries set to be as exciting as Super Tuesday, Michigan could prove to be the most important moment yet in Romney's presidential bid as he struggles to maintain hold over his frontrunner status.
Santorum has won three of the last five states and is showing staying power far beyond his team's finances and organisation. If Romney loses both primaries on 28 February and the Washington caucus, for which polling predictions suggest a close race, it would be his sixth loss in seven contests heading into Super Tuesday - all to Santorum.
With everything to play for, tonight's debate in Arizona could be monumental and there's no doubt that both Santorum and Romney will be hoping for homerun performances in what could be a decisive turning point for both campaigns.