The Gunners lost at Tottenham on Sunday to fall seven points behind their North London rivals.
"On our day we can beat anyone," Jenkinson told Arsenal's website.
"I genuinely believe that. When we play to our potential, teams can't come near us, but we need to do that consistently.
"If we do that we will be fine, but we just can't find the consistency at the moment.
"We played well (against Tottenham) in patches, but then we'll have 10 minutes where we'll drift out of the game a little bit."