He abruptly pulled out of Iraq, leaving a power vacuum that ISIS and Iran quickly moved into.
His actions in Libya cratered that government, too, and another formerly-stable region fell into radical Muslim hands.
He stood by while Egypt and Syria fell into chaos. Both are on their way to being the same kind of fundamentalist anarchies.
He and John Kerry gave the Iranians everything they wanted to complete their nuclear program, and $150 Billion besides, which they are currently spending on armaments from the Russians.
All this is happening all around the Saudis, who see the balance of power moving markedly away from them. If Iran and ISIS join forces they've already got SA surrounded and threatened on every side.
I'm sure Obama is going there to reassure the Saudis, promising to support and help defend them. But why should they believe him?
Probably something like:
"As you know, I've been working on America's defeat for the past 8 years. Next February, a coalition of 27 terrorist nations and groups will launch the first wave attack on the USA. Here's a list of 1,235 sensitive targets in the US. Please assist by doing all you can to help defeat the Great Satan".