The ‘spoiler effect’

The possibility of New York Mayor Michael Bloomberg entering the US presidential race will resuscitate talk of the 'spoiler effect', which describes the destabilising impact a third-party candidate can have on a close election. Candidates who are unaffiliated with either the Republicans or Democrats offer a different choice to voters who are unwilling to vote for either major party. They draw votes away from the major-party candidate that has the most ideological similarities to them.  This sometimes gives the other major-party candidate a decisive advantage at the polls.

The 2000 US presidential election is a case in point. Green party candidate Ralph Nader's presence in the race probably swung Florida and New Hampshire to George Bush, when a win in either state would have pushed Al Gore over the 270 electoral vote threshold needed to win. Bush won just 537 more votes than Gore in Florida. Yet many of the vice president’s supporters believe that had Nader not been in the election, most of his 97,421 Florida votes would have gone to Gore.

It is popularly belived that Reform party candidate Ross Perot had the same effect in 1992, as the conservative vote split between him and the elder George Bush, allowing the Democratic candidate, Bill Clinton, to capture the presidency. However, the result would not necessarily have been measurably different in Perot's absence, as initial voter interest in the Texan businessman came primarily at Clinton's expense.

Bloomberg: more than a ‘spoiler’?

Nader is flirting with the idea of a fourth successive presidential campaign, a prospect that irks Democrats, who still blame him for scuppering Gore's White House bid. But Republicans have more reason to worry about Bloomberg entering the race. Although independent candidates realistically have no chance of winning presidential elections, they can act as unwitting kingmaker in drawing votes away from the candidate they most resemble. Evidence suggests Bloomberg will hurt the Republican candidate the most if he chooses to run – especially if that candidate is Bloomberg’s predecessor as New York mayor, Rudolph Giuliani. Yet while Bloomberg’s huge personal fortune gives him the cash necessary to finance an independent bid for the presidency, he will likely prefer to stay out of the race unless he sees a possible path to victory.  Unlike Nader, Bloomberg would want to win -- not just play the 'spoiler'.