An uptick in murders across the country is testing their resolve — and their electability.Philadelphia District Attorney Larry Krasner blames larger societal forces for the spike in homicides — which are up 29 percent compared with this time in 2020. | AP Photo/Matt RourkePHILADELPHIA — Larry Krasner’s election in 2017 was a triumph for progressives nationwide: The man who had sued cops 75 times, represented Black Lives Matter, promised to end cash bail — and was widely seen as the most liberal district attorney candidate in the country — won.Four years later, Philadelphia’s top prosecutor...…An uptick in murders across the country is testing their resolve — and their electability.Philadelphia District Attorney Larry Krasner blames larger societal forces for the spike in homicides — which are up 29 percent compared with this time in 2020. | AP Photo/Matt RourkePHILADELPHIA — Larry Krasner’s election in 2017 was a triumph for progressives nationwide: The man who had sued cops 75 times, represented Black Lives Matter, promised to end cash bail — and was widely seen as the most liberal district attorney candidate in the country — won.Four years later, Philadelphia’s top prosecutor...WW…