washington hard-line republican effort impeach top u.s. tax collector come fire tuesday democrats call unsubstantiated partisan attack could undermine credibility congress internal revenue service commissioner john koskinen face allegations house judiciary committee ignore congressional subpoena mislead lawmakers accusations stem 2013 scandal irs criticize target conservative tea party group applications tax-exempt status extra scrutiny republicans want republican-controlled u.s. house representatives vote impeach koskinen congress leave midyear break july democrats oppose effort resolution fail every measure arise bad partisan instincts base facts representative john conyers say outset first two judiciary committee hear examine charge koskinen vote impeachment divide party line ... undermine credibility add conyers panel top democrat koskinen anger critics decline testify submit statement say charge without merit fail meet constitutional impeachment standard treason bribery high crimes misdemeanors absence committee hear republicans house oversight government reform committee investigate tea party scandal conclude koskinen fail preserve evidence late destroy really simple case mind congress ask question expect give truthful answer congress issue subpoena compliance optional house oversight panel chairman jason chaffetz testify chaffetz describe impeachment remedy congress officials guilty breach public trust democrats note irs federal bureau investigation probe produce evidence criminal wrongdoing deliberate efforts mislead congress say case koskinen show little agency mismanagement misstatements judiciary committee chairman bob goodlatte offer direct criticism impeachment push avoid use term name impeachment one several options include power write laws power purse ... power censure republican push impeach u.s. irs chief hit democrats