With polls indicating this year’s race for the White House will be highly competitive, the key decision Mitt Romney has to make before the Republican presidential convention in August is his choice of running mate. Wide-ranging candidates are being touted in the media, including US Senators Marco Rubio and Rob Portman, Governors Mitch Daniels and Tim Pawlenty, and even Hewlett Packard CEO Meg Whitman.

The vice-presidential selection process is an election year custom that attracts high prominence, partly because of several key changes in US politics in recent decades. Firstly, the vice-presidency has become the single best transitional office to the presidency. Secondly, the office of vice-president has assumed more power and resourcing. And thirdly, the electoral stakes have grown of not selecting a deputy who is perceived to be capable of assuming office effectively upon the incumbent’s unanticipated death or incapacity.

This latter factor was a major feature of the 2008 presidential election when Republican nominee John McCain, aged 71, made the high-risk decision to select Sarah Palin – whose only major experience of office was less than two years as Governor of Alaska. Rather than boosting McCain’s campaign, Palin was – ultimately – widely viewed as too inexperienced to be president. This was also true in 1988 of Dan Quayle, then a two-term US senator, who was selected by George H.W. Bush.

In light of the Palin episode in 2008, Romney will be keen to make a choice that will "do no harm" to his electoral prospects. Hence, part of the reason why Portman and Daniels, with their wide-ranging political experience, have received so much attention from media.

Historically, the process of selecting vice-presidential nominees tended to be fashioned around issues like reconciling important party stakeholders after what can be bruising nomination contests; and the perceived advantage of cultivating so-called ‘balanced tickets’ in which the vice-presidential and presidential candidates where differentiated by factors such as their ‘home’ region of the country, or philosophical wings of the party, so as to maximise support across the nation.

One potential balanced ticket candidate for Romney is Rubio, whose life story – he was born in Florida to Cuban immigrants – potentially contrasts favourably with perceptions of Romney’s wealth and privilege. Rubio is also a Tea Party favourite, potentially neutralising conservative concerns about Romney’s more moderate Republicanism. The selection of Rubio, while containing the potential hazard of his relative national political inexperience (he only entered the US Senate in 2011), would also increase the prospects of Romney winning the key swing state of Florida.   

Romney’s wife, Anne, also enthusiastically highlighted earlier this month that Romney might choose a woman. As well as Whitman (who stood as the Republican candidate in the 2010 Californian gubernatorial election), potential female candidates touted in the media include three who, like Rubio, are serving only their first term of office in their present post: US Senator Kelly Ayotte (who represents the swing state of New Hampshire); South Carolina Governor Nikki Haley (an American-Indian whose parents emigrated from Amritsar); and New Mexico Governor Susana Martinez (who could potentially appeal to the rapidly growing US Hispanic population). 

However, partly because of the changes in the presidential nomination system, and indeed the proliferation of mass media, these traditional considerations (while still of enduring consequence) are less relevant to the modern process. Thus, Al Gore was selected in 1992 by Bill Clinton (a fellow centrist Democrat and southerner) not to balance the ticket, but instead to reinforce a key narrative about Clinton’s "New Democrat", change candidacy.

Whether or not these developments have potentially injected greater uncertainty into the vice-presidential selection process, it is unquestionably the case that choices are routinely made that confound the pundits. For instance, few (if any) anticipated the selections in 2008 of Palin and Joe Biden, nor in 2000 of Dick Cheney and Joe Lieberman.

The selections of Washington veterans Cheney and Biden (who looks likely to Obama’s running mate again this year) were noteworthy inasmuch as they were chosen, in significant part, to fortify the national and international political inexperience of George W. Bush and Barack Obama. Cheney, in particular, therefore assumed a high profile role as vice-president, and is widely viewed as the most powerful ever holder of the office.

Cheney’s influence partly derived from his experience and connections as a former White House chief of staff; congressman and defence secretary, and the innovations he brought to the office of the vice presidency – for instance, he considerably increased his national security staff. However, his influence also reflected the increased status of the vice presidency in recent decades which, as well as being reflected in larger staff budgets, also includes greater proximity to the centre of power through a West Wing office in the White House; weekly one-on-one meetings with the president; and authority to attend all presidential meetings.

The selections of Cheney and Biden were also interesting in another sense: both George W. Bush and Obama made the assumption that neither of their more experienced running mates represented a political threat to them, and would thus be very loyal, because they were too old (and in Cheney’s case suffered from too poor health) to run for the presidency themselves in the future. Seen from the prism of the last few decades, this is highly unusual.

Indeed, since 1960, four sitting vice-presidents (Richard Nixon in 1960, Hubert Humphrey in 1968; Walter Mondale in 1984; and Gore in 2000) won their respective party’s presidential nomination but then lost the general election, whilst two vice-presidents have been elected president (Nixon in 1968 and George H.W. Bush in 1988). One reason vice-presidents have, in the post-war period, enjoyed particular success in securing their party’s presidential nomination relates to the Twenty Second Amendment in 1951.

This constitutional amendment restricted presidents from serving more than two terms. Importantly, for vice-presidents, this allowed for the possibility of organising a presidential campaign in the sitting president’s second term of office without charges, from inside or outside his party, of disloyalty.

It is thus in this context of short-term political calculation and historical precedent that Romney will make what could prove his defining decision of the campaign. Miscalculation could prove damaging, especially if the race remains tight. However, if the selection wins strong approval, his candidacy will secure invaluable new momentum.

Andrew Hammond was formerly the North America Editor at Oxford Analytica, and a UK Government Special Adviser.