Ted Cruz's early pick of Carly Fiorina as his potential running mate reeked of desperation, anything to get a few free headlines away from Donald Trump in these final few primary battles.

Any maybe Fiorina can help him in the all-important California primary, though the purpose of the VP is generally to enhance winning chances in the general election, not shore up a dwindling, almost futile last ditch effort to spoil the primary election and force a brokered convention.

While Cruz's goals may have been predominately shortsighted, usually a lot of thought goes into a VP tap -- and how the pick can shore up weaknesses and enhance the nominee's chances of winning in the general election.

1. The VP Tap Must Assume the Role of the Nominee's Faithful Attack Dog--Defending Policies While Keeping the Candidate Above the Fray

When looking at the past two presidents, in particular, this axiom was very true. Both VPs Biden and Cheney served their roles of 'enforcer' well; both were superior general election debaters of the president's platform.

Their loyalty is often seen as completely flawless, even if they don't 'get along' with the presidential candidate. They are a personification of loyalty to both the party and the nominee.

2. The Successful VP Tap is Almost Always a Strong Political Insider with Considerable High Level of Experience

Since WWII, the 13 elected VPs have had a lot of political experience, mostly in the Senate (10 total, which makes sense since they become the President of the Senate), but also state governors (2), House leadership (1), and high-level cabinet posts (2).

Often the president provides the vision of policy, while the vice president has to form a coalition of support in the Congress to advance the agenda.

3. The Successful VP Tap 'Completes' the President

Barack Obama had serious troubles with the rank and file Democrats during the 2008 election -- after winning overwhelmingly by capturing the youth and independent vote.

He needed a party insider -- Joe Biden.

Often it's not just political credibility at stake. For instance, the adage, 'it takes a Southern Democrat to win the White House' has inspired some choices in VP picks to enhance Southern credibility -- or to balance the ticket with a solid Northerner (like Humphrey and Mondale).

And most often in modern politics, the VP pick covers your political base. Both Presidents Clinton and G.W. Bush were seen as too moderate by their respective parties. Gore and Cheney served to cover their political base and meet the needs of the party-hardliners, leaving the nominee free to invite the center and swing voters to the political fold.

4. Most Successful VP Taps Aren't Running for POTUS Themselves

Most of the time, the nominee does not pick someone from the primary pack to enhance their ticket, and if they do, they almost always pick the runner-up or someone who withdrew in the earliest stages of the contest.

Why?

Two immediate reasons for this are easily apparent:  You don't want a perceived 'loser' on the ballot with you and you don't want to give your opponents unnecessary fodder during the general election by giving them attack lines used against two 'now unified' running mates.

This only makes sense. It's hard to distance yourself from comments like Fiorina's directed at Cruz during the primary, stating that:

He says whatever he needs to say to get elected, and then he's going to do as he pleases, I think people are tired of a political class that promises much and delivers much of the same.

It's hard for anyone running against such a pair to not use the animosity of the primary season against them -- and show the apparent hypocrisies in their campaigning.

5. Youthful Energy and the Gravitas of Wisdom and Experience

It's rare to see two young politicians on the same ticket like we saw in the pairing of Clinton-Gore in 1992.

Usually, a younger presidential candidate seeks out an older, experienced running mate with a perception of wisdom and experience, and vice-versa (Obama-Biden, Bush-Cheney, Bush-Quayle, JFK-LBJ -- to name a few).

As with everything listed so far, the VPs role is to balance the ticket, to attract as many voters as possible to the ticket including the moderates, center, and swing voters.

6. With all of This, the VP has to Accommodate the Changing Demographics in America

Gone are the days of the VP being characterized as a 'white male's job.'

Recent history, including John McCain's tap of Sarah Palin in 2008 has shown that the demographics of the VP are changing just as quickly as those of the presidency.

Donald Trump could force the issue and make 2016 become the first election in history with women on both party's tickets at the same time, which would also help increase his image among women voters.

Both candidates are likely to consider a Latino running mate; it is simply too powerful of a voting bloc at this point to be ignored.

Yes, 2016 could see many firsts in demographics as the vetting process for the presumed nominees unfolds.

Even With all of This, VP Taps Often Dictate Policy in Unexpected Ways

Joe Biden forced President Obama to deal with the gay marriage issue, an issue that Obama had been quite content to keep on the political back burner.

Biden forced it into the open, and the president at that point had to deal with the reality that his VP had dictated presidential policy on the issue.

This is far from rare.

Dick Cheney largely directed the Bush administration's foreign policy agenda, including making the case for war against Iraq.

Al Gore kept President Clinton on task with many politically unpopular aspects of the liberal agenda, like climate change and environmentalism.

But for a VP tap to be successful at doing this, they can't be a president's 'yes-man' or political mirror--instead, this is part of the natural evolution of a VP tap completing the president by often having additional agenda goals that are popular within the base.

Strangely, in 2016, it seems that the front-runners are going to be picking vastly different types of running mates for the general election.

Clinton has moved so far toward the progressive agenda that she will need a moderate Democrat to anchor her credibility with the rank and file, as well as independent voters.

Trump desperately needs a political insider to counter his 'off-the-cuff' style campaigning, someone who is a seasoned politician with established track-records and goals.

A well-picked running mate could be the deciding factor in the 2016 election, either making a dream ticket that invites all to participate, or creating a ticket of party cronyism -- one where political favors in the party were seen as more important that voter preferences.

In the end, 2016 could come down to how well the candidates pick their running mates--and both parties need to consider how they can invite disenchanted outside voters into the fold come November.