"Double Down" ---> New word of the day

"Double down", "double down", "double down!"

I have heard this phrase thrown around so many times in the last few months during the American election season. So what does this phrase mean, exactly? 

• To increase one's efforts or focus
• Going to try twice as hard
• To double the bet after one has seen the initial cards, with the requirement that one and only one additional card be drawn
• To engage in risky behaviour, esp. when one is already in a dangerous situation
• To commit oneself even further, even though one is already in a risky situation
• Original incarnation. A gambling term from blackjack, it describes a strategy in which a blackjack player who is sufficiently convinced of the strength of his hand can choose to double his original bid. In this context, "doubling down" means making a calculated gamble in order to maximize the potential yield of a project.