Republicans insist Gov. Gavin Newsom of California isn’t a threat to the Trump presidency. White House allies argue privately that he’s too liberal, too manicured and just too California to win a national election. And yet: They also acknowledge this week that Newsom looks more politically formidable than at any other point in his career. One Republican strategist said Newsom’s winning redistricting campaign in California transformed him into a top rival of Donald Trump,” while another conceded it had cemented him as a “Tier 1 Democrat.”