shaky
adjective
uk/ˈʃeɪki/ usnot in good condition or likely to fail:
The government is taking these steps to try to improve the country's shaky economy.
Too many mortgages were given to people with shaky credit histories.
Several of the big life insurance companies are looking shaky.
on shaky ground
in a situation in which there is a strong possibility that something might stop working, be defeated, etc.:
The state's finances are still on shaky ground.
I think you're on very shaky ground with that argument.