Anecdotally, it seems as if some of the fight has gone out of the Never Trump movement this week. Anti-Trump Republicans have continued to blast away at their nemesis in the press and on the Internet, but Trump's multiple electoral victories on Tuesday have dimmed his critics' hopes that Republican primary voters will rally around the two other remaining candidates in order to send a clear sign that they, too, find Trump an intolerable choice for the nomination.
Whether Trump will actually gain an outright majority of pledged delegates remains mathematically unclear and probably will not be resolved until June 7, the final date on the primary calendar, when delegate-rich California and New Jersey have scheduled their primaries along with three smaller states. But we can conclude at this stage that Trump is positioned to hold a delegate plurality at minimum, and with it the standing to argue that he, as the first choice of Republican voters, cannot rightfully be denied the nomination.
One set of issues raised by the prospect of a contested convention is procedural, encompassing party rules (and their interpretation and possible revision), the selection of delegates, and so forth. But another set involves the question of legitimacy: whether the national party organization has the "right" to block the popular choice of the Republican electorate from receiving its presidential nomination, and whether doing so would or would not cause more damage to the Republican Party—both in the short and long term—than ratifying the expressed preference of party members.
Given the magnitude of the threat posed by Trump to much of the existing Republican leadership, it is somewhat remarkable how little open resistance there has been (one short speech by Mitt Romney does not really constitute a party-wide revolt). It is possible that party leaders are quietly confident that Trump can be defeated down the road; more likely, they are more or less resigned to a Trump nomination unless the voters themselves shift against Trump in the remaining primaries. This behavior suggests the existence of a powerful norm respecting the perceived democratic legitimacy of the primary process even when it results in a deeply undesirable outcome.
Put simply, Republican leaders are unlikely to risk building a coordinated effort to block Trump at the convention unless they feel as if the voters are behind them. If Trump's support were to decline significantly in the later primaries, so that he barely crawled across the finish line with a plurality of delegates, anti-Trump forces might be emboldened to carry the fight to Cleveland. Alternatively, if the Republican electorate as a whole expressed obvious buyer's remorse—for example, if a majority of Republican identifiers told pollsters by July that they supported an effort to discard Trump in favor of an alternative candidate—the anti-Trump Republicans could claim a popular legitimacy of their own to rival that conferred on Trump by the electoral process.
Absent such signals from the voters, however, the usual presumption that a first-place candidate should rightfully claim victory is likely to hold—and a demoralized Republican leadership will reluctantly acknowledge that the people have spoken.