Donald Trump’s selection of Breitbart Media chairman Stephen K. Bannon as his campaign’s new chief executive made official a role Bannon has played from afar for the past few years — that of ideological soulmate and cheerleader for the Republican nominee. Trump’s appointment of Bannon on Wednesday will probably intensify whatever hard feelings already exist the between Trump and the GOP’s other leading figures during the campaign’s final months. It also seems more likely to help Trump among the “insurgent” wing of the party than among the independents and moderates that Trump will need to defeat Hillary Clinton in November.