Took out my P938 for its 2nd range trip this past weekend to run a couple hundred more rounds through it.  Was hoping the trigger smoothed out a little more.  Brought it home to clean it afterwards and accidentally pushed the front site post over with my thumb.  

Called CS and they said it is normal to be able to drift a front site post like this (medium amount of force), but I could still send it in to be looked at if I wanted.

It has 2 stopping points pictured (site post in the middle - pictured above) and (site post to the right pictured below).  It will slide back and forth with very little resistance between the 2 points.  I am unsure if the top picture is how the site was positioned while I have been firing it.  Using degreaser on the slide to clean may have broke it free.

TL;DR - front site post can drift with force applied with thumb.  Two stopping points pictured; post drifts between those two points with little resistance.  normal?  send back?

I am leaning towards sending it back.

I had to on my 938 sport I bought last year due to it doing this when my wife fired it and took out the target holder while focusing on the fiber optic after the first few rounds of a mag.  Luckily we caught this before I used it in a life or death situation.  Took like 2 weeks to get back when they fixed it.  Now it hasn't moved since it was repaired, crossing my fingers it stays that way.

Try staking it or Loc-Tite. Or send it back to Sig.

I think I am just going to send it back.  I thought about trying to add Loc-Tite; but thought a degreaser might make it break free again.  Since this will be my primary carry weapon for the summer I wanted to make sure the front site post was rock solid.

Agreed, new pistol and all.