double down

verb2

1. •
   To double one's wager, particularly, the name of a specific doubling bet allowed in blackjack.

   • He'd bet three thousand and double down to six thousand, all of it hanging on the turn of the next card. — 1999
2. •
   (figurative) To significantly increase a risk, investment, or other commitment; to respond to a challenge (e.g. to an opinion) by reinforcing or extending one's position rather than moderating it.

   • Hillary Clinton, John Edwards and Barack Obama all want to get out of Iraq. They all want to double down in Afghanistan. — 2007