This article explores whether different media platforms across impartial news media supplied the same level of scrutiny in how they fact-checked political claims. While prior research has largely focused on independent fact-checking organisations, the fact-checking practices of legacy media through a cross-platform perspective have comparatively received limited attention. The study develops new lines of inquiry into the fact-checking practices of legacy media, presenting one of the largest and most forensic cross-platform studies of fact-checking to date. It draws on a systematic content analysis of 355 items from fact-checking sites, including 689 claims and 1850 instances where journalists or sources interacted with them in 2021, and assesses how they were covered by a further 280 television news items. Our findings demonstrate that the selection and degree to which journalists and sources scrutinised political claims varied across media platforms, with television news less inclined to report and analyse policy claims than dedicated fact-checking websites. Overall, we argue that the editorial boundaries of fact-checking are policed by journalists' interpretations of impartiality, which differ across platforms (in television news or dedicated fact-checking websites) due to a range of editorial factors such as production constraints and news values.