▁whole . ▁ ▁M enz ies ▁retired ▁in ▁ 1 9 6 6 ▁and ▁was ▁succeeded ▁by ▁Harold ▁Hol t . ▁Mc E wen ▁thus ▁became ▁the ▁longest - ten ured ▁member ▁of ▁the ▁government , ▁with ▁the ▁inform al ▁right ▁to ▁v eto ▁government ▁policy . ▁The ▁most ▁significant ▁instance ▁that ▁Mc E wen ▁exerc ised ▁this ▁came ▁when ▁Hol t ▁disappeared ▁in ▁December ▁ 1 9 6 7 . ▁John ▁G orton ▁became ▁the ▁new ▁Liberal ▁Prime ▁Minister ▁in ▁January ▁ 1 9 6 8 . ▁Mc E wen ▁was ▁sw orn ▁in ▁as ▁an ▁inter im ▁Prime ▁Minister ▁pending ▁the ▁election ▁of ▁the ▁new ▁Liberal ▁leader . ▁Log ically , ▁the ▁Liber als ' ▁deput y ▁leader , ▁William ▁Mc M ah on , ▁should ▁have ▁succeeded ▁Hol t . ▁However , ▁Mc M ah on ▁was ▁a ▁sta unch ▁free - tr ader , ▁and ▁there ▁were ▁also ▁rum ors ▁that ▁he ▁was ▁hom osex ual . ▁As ▁a ▁result , ▁Mc E wen ▁told ▁the ▁Liber als ▁that ▁he ▁and ▁his ▁party ▁would ▁not ▁serve ▁under ▁Mc M ah on . ▁Mc M ah on ▁stood ▁down ▁in ▁favour ▁of ▁John ▁G orton . ▁It ▁would ▁be ▁only ▁after ▁Mc E wen ▁announced ▁his ▁ret irement ▁that ▁Mac M ah on ▁would ▁be ▁able ▁to ▁successfully ▁challenge ▁G orton ▁for ▁the ▁Liberal ▁leadership . ▁Mc E wen ' s ▁reputation ▁for ▁political ▁t ough ness ▁led ▁to ▁him ▁being ▁nick named ▁" Black ▁Jack " ▁by ▁his ▁al