A good place to start this exercise is by looking at 2004 exit polls:
|Group||% of Electorate||% Kerry|
In 2004, African Americans comprised 11% of the electorate while Hispanics made up just 8%. While 88% of African Americans voted for Kerry, only 53% of Hispanics did so (though this figure has been disputed to some extent). The 53% figure was rather low and rebounded in 2006, when nearly 70% of Hispanics voted for Democratic congressional candidates.
The first step is to figure out what the composition of the electorate would be in 2008. Let's begin by assuming that turnout among African Americans and Hispanics would be higher since there would be a black and Hispanic man on the Democratic ticket. The Pew Hispanic Center estimates that Hispanics will make up 9% of the eligible electorate in 2008. Let's assume that with Richardson on the ticket, their turnout is comparable to their share of the eligible electorate. Let's also assume that with Obama running for president, that African Americans comprise 12% of the electorate in 2008. So, under these assumptions, the electorate would look something like this:
|Obama/Richardson||% of Electorate|
Based on this hypothetical electorate, let's produce two scenarios. First, let's assume that an Obama/Richardson ticket would win the same level of support among whites that Kerry won in 2004. However, let's also assume that they would win 90% of the black vote and 80% of the Hispanic vote (10% better than Democratic congressional candidates did in 2006). Under those assumptions, Obama and Richardson would carry 51% of the popular vote.
Second, let's take the worst case scenario for the Democrats and assume that this ticket would lose some support among whites. Let's assume that Obama and Richardson would do 5% worse among white men and 4% worse among white women. If that were the case, then they would capture just 47% of the vote, which would obviously fall short of victory. In other words, increasing Hispanic support from 55% to 80% would be off-set if support among whites dropped by just 4-5%.
But which of these scenarios would be more likely? In many ways, it is hard to imagine that support for a Democratic ticket could decrease among any demographic group in a year as favorable for Democrats as 2008. This suggests that scenario 1 may be more likely. Then again, it is hard to know for sure how this would play out. More importantly, there are a lot of high profile names out there for the position, so we likely will never know how an Obama/Richardson ticket would have fared.