With the topic reaching a fever pitch lately, let's just make it clear. I've been saying off and on since late February that Trump's criteria for VP, which he has repeatedly gone through to interviewers, lead toward Jeff Sessions.
He's the most similar to the future President on policy, and Trump has said that's the most important thing -- to be a faithful back-up, just in case.
He has decades of experience in the Senate, which experience Trump wants in order to hit the ground running on passing legislation.
He's been working with Trump for over a year, before the campaign was formally announced, meaning they have history and loyalty, something Trump requires.
He doesn't pick up any swing states, but voters are choosing Trump at any rate, not the VP.
He does provide geographic balance, and personality balance, being a soft-spoken Southerner.
Many people thought this as well, so it did not take any brilliance on my part -- just putting two and two together. This recent tweet by Roger Stone would seem to confirm it.
These clues are based on substance (who stands where on which policies), but you could also have figured it out from the showmanship that Trump is also an expert at. Back in late February when Sessions formally endorsed Trump, he was brought out to a massive rally in his home state of Alabama.
Most folks at home aren't political junkies, and would have had little idea who he was or what he stood for. So why was Trump shining such a spotlight on him, and at such an early stage? He wanted us to get familiar with him, something that he's enhanced over the months by naming him as a top policy advisor (gets him into the news cycle), and sending him to do interviews on the cable news circuit.
Why else would Trump want us to get so familiar with Sessions? He wants the VP announcement to be somewhat of a surprise -- hence feeding the gullible media all sorts of red herrings -- but he doesn't want that person to be an unknown, which would disorient the voters and perhaps start us worrying about who this guy is and what he stands for.
Come the Convention in Cleveland, voters will have seen and heard enough from Sessions himself, to feel familiar with the choice.
Trump knows how to tell a proper story and put on a good show, so he made sure to set up the announcement of Sessions as VP way back during the early primary stage, like Chekhov's gun. Notice that the other major endorsements did not receive as much fanfare, and the endorsers have not been a recurring presence in the media to stump for Trump. They have been important additions to the story, but not absolutely crucial like the role of Sessions.