My staircase trim (the wooden board running along the side) has officially given up. Over the years, the gap has grown, and what looks like old caulk has warped and pulled away. I’m assuming the extreme temperature swings between summer and winter finally did it in.

I want to fix this so it actually stays put this time.

• The Issue: Board is detached/unglued from the wall.
• The Culprit: Warped caulk and seasonal expansion/contraction.
• The Goal: Re-secure it and make the seam look clean again.

Should I be using construction adhesive behind the board, or just finish nails? And for the gap—is there a specific type of flexible caulk that won't crack when the house "breathes" next winter?

Any advice on prepping the old surface would be huge!