should China join first

[Maybo]

But it warned that its bid to join the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP) could be put at risk should China join first. (Taiwan seeks entry into key trade pact before China by BBC)

I don't understand the sentence structure - the "should" part.

 

[probus]

"Should China join first" is the same as "if China joins first".

 

[Tdol]

It's an alternative form of the if- clause in a first conditional:

If it rains
Should it rain