Mike Pence for Vice President?
It is extremely unusual that being nominated to run as a major party's candidate for Vice President would be harmful to the person accepting the nomination, but that is what would be the case for Mike Pence. There are positives, of course, but there are enough negatives that this would ultimately be a bad career move for Indiana's governor.
The most obvious problem is this: Donald Trump is a raging dumpster fire. As Trump's running mate, Pence would be obligated to defend Trump throughout the next three and a half months. Trump has said and done a number of outrageous things over the last year and is still not trusted by even a lot of Republicans who support him. By attaching himself to Trump, Pence would be accepting Trump's baggage as his own. It would be very difficult to walk that back after the election is over, and if Pence tries to do so he may wind up looking worse in the process.
If Trump wins, Pence gets the prestige of being Vice President but would be further saddled with Trump's antics. If Trump acts illegally to restrict free speech or due process, or attempts to force the military to commit war crimes, Pence would be tarred by that too. One lesson for Pence is that Bill Clinton's antics in office harmed Al Gore in 2000. Pence would not have the perch of the Vice President's office from which to launch his campaign if he avoids Trump, but he would also have a cleaner record in running for President in 2020 or 2024.
Indiana is a Republican state, and Pence has a financial advantage over his opponent in a rematch of 2012. Hillary Clinton is deeply unpopular here, so even with Trump leading the ticket the Presidential race is likely to have at least a net neutral effect if it is not a positive for Pence. Indiana's economic climate is strong and that always helps the incumbent. Trump's ability to win the Presidency is questionable at best, so Pence would be taking a safer bet by staying where he is instead of joining forces with Trump.
Some Republicans think moving Pence would be useful because of the Religious Freedom Restoration Act (RFRA) controversy last year, but in terms of Indiana politics that has pretty much played itself out and will probably not be a factor in the 2016 election. If Pence becomes Trump's vice presidential nominee, RFRA will be re-litigated not only in Indiana but all across the nation as well. I do not buy the argument that RFRA damaged Pence, and the only people still motivated by it are people who would never vote Republican anyway. There is no need to make that a distraction going forward, though.
No matter who replaced Pence on the ballot, choosing a new candidate for governor with handicap the Republican Party's chances of holding onto the seat. Pence already has a strong campaign infrastructure in place, so a new candidate would have to build a statewide campaign and start winning voters with only two and a half months before early voting starts. Sure, some of that can be transferred but throwing the ballot into chaos with only two and a half months to go would hurt the party. Pence needs to consider what he would be leaving behind and if his replacement loses some Republicans may hold a grudge.
Pence has a lot to lose by going with Trump, both in the short term and in the long term. There is a significant upside, of course, but that depends on how Trump behaves over the next four years - something that is by no means predictable and could actually be harmful. Pence would be wise to respectfully decline and pick the safer bet of staying on as governor.