if it comes to the crunch

If it becomes critical. Related to "crunch time," which is a critical period of time characterized by a heightened pressure to succeed, usually at or near the end of a given situation or undertaking. If it comes to the crunch, I can ask my dad for the money. I don't like either solution, but if it comes to the crunch, I think our best bet is to consolidate the companies into a single entity. The candidate's polling numbers are not great. If it comes to the crunch, we'll have to get an alternative into the race instead.

if/when it comes to the ˈcrunch

(informal) if/when the moment comes when something must be decided or done, or a difficulty can no longer be avoided: She was always threatening to leave him, but when it came to the crunch she didn’t have the courage.