In terms of a PVI-shocker, it'd be similar to a Southern Republican winning California in 2016 in a moderate national victory.
A Huckabee / Martinez ticket can do it if the Democrats put up a hard left candidate like Elizabeth Warren who has a very weak campaign message and a horrible running mate like Kirsten Sinema who I can see easily becoming the Democratic Sarah Palin.
Of course this scenario is very unlikely but it can happen. No one expected the GOP to lose every state except for the Deep South (then a solid Democratic region) and AZ in 1964. Consider Huckabee's strong appeal among minorities (IIRC he was one of the only Republicans to win the black vote in recent times and this could be very beneficial in California considering the majority of blacks and Latinos voting for Prop 8.) and Martinez being a very popular governor in a Latino-majority state. A splitter left candidate (Bernie Sanders has hit a run) could seal the deal for the GOP in this scenario.
