To "cool one's heels" -to be forced to wait a long time at some place, like a busy doctor's office or at an employment agency looking for a job.

“晾脚后跟”指一个人被迫在某地等候很久，如在忙碌的医生的候诊室久等，或在职业介绍所等待工作。

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But he's got one week to do that, and a serious challenger nipping at his heels before the March 7th primary.

NPR: DeLay Faces Tough Texas Primary Challenge