hammer away at
Keep at something continuously, as in The reporters hammered away at the candidate. This phrase employs hammer in the sense of “beat repeatedly,” a usage dating from the mid-1600s.
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The American Heritage® Idioms Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.