The empirical data does not follow with your conclusion. It shows that home-state advantage can amount for substantial gains in particular states.
There are numerous aggregates the show this...
Here is an analyst of Mitt Romney's 2012 VP selection options and their predicted influence (net) on the state's popular vote when factoring home-state favorability:
As you can see, for the vast majority of candidates, there is a predicted positive impact on state voting.
The vetted candidates for Romney at the time were Rubio, Christie, Bush, Toomey, Portman, Ryan, McDonnell and Pawlenty.
Romney's team looked at these numbers and made a logical choice based on a few factors:
Premise: Romney's weakness is with the Republican
base, social conservatives, including evangelicals and particularly Catholics who might not vote for a Mormon candidate.
1) They believed they would need to win Florida by themselves; and that if they couldn't, then the rest of the states didn't matter. This was a logical, but flawed strategy.
2) That Portman was too liberal, and would not bring Ohio while likely alienating social conservatives.
3) That Pennsylvania was blue; regardless of what the media says for entertainment value. (-Toomey)
4) That Bush wants to be President in 2016, not Vice President in 2012 or running on a failed ticket.
5) That New Hampshire, New Jersey and Nevada were out of reach.
6) McDonnell was the most logical choice, being a popular governor; but he did get through the vetting process.
So Romney's team was left with few options.
The best choices remaining are Rubio, Bush (w/terms), and Ryan.
If I were ranking those choices I'd likely pick:
-Rubio
-Bush
-Ryan
Romney was not interested in negotiating terms with Bush, and even though Rubio desperately wanted the nod; Romney never seriously considered him as being "ready to lead on Day 1." His reasons are believed to have been more personal.
These two men do not like each other, and Romney felt that Rubio's position on immigration (at the time being much more liberal than it is today) would not resonate with conservative voters. There was also fear that a Mormon/Cuban ticket would not bode well in the South.
Romney's pick was Pawlenty - but his team strongly advised him to pick someone who shored up his weaknesses with Catholics and the Republican base, and Pawlenty did very little in that regard. So the team settled on the bright, telegenic, and smart Paul Ryan, a devout Catholic, ultra pro-life conservative which the base loved.
It wasn't the worst pick, but had Romney went with Rubio or Bush, or if McDonnell wasn't under investigation at the time, Romney would have had a better shot.
For example, in 2012, Barack Obama won Florida by less than 75,000 votes.
Obama won 48% of the Cuban American vote in Florida, up from 35% in 2008 in just 4 years, on a less than stellar campaign.
Had Romney picked Rubio, he would not have needed to campaign in Florida as much only to lose and could have put that campaign money to better use in Ohio and Virginia.
So yes, the VP nomination makes a huge difference to the prospects of the ticket. This other person on the ticket is doing 50%+ of the campaigning. Rubio is well liked in Florida, and brings the demographics you need to win that state. He's also young, Catholic, and pro-life and he can resonate with Catholic voters.
Romney made a mistake by not picking based on the above information and assuming he could get by with Pawlenty or Ryan.
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