Canal - Capablanca, Budapest 1929

There was one other game that made a deep impression on me in Chernev's Logical Chess: Move By Move.  In Canal-Capablanca, Budapest 1929, it sure looked like Capa was in trouble.  (And indeed FireBird suggests a moment or two where White may have missed an opportunity for advantage.)

Chernev is silent on White's big mistake:

Canal-Capablanca, Budapest 1929

After 31...Ra1

White to move

Black's next couple moves are fairly easy to predict: ...a3, ...a2, ...Rook moves somewhere (with check or attack), and ...a1=Q.  

How can White interfere with this plan?