The biggest development in last night's debate was that Donald Trump was treated like the front-runner he has become. Rather than fight among themselves to claim status as the #1 alternative to Trump while letting Trump himself off easy, Marco Rubio and Ted Cruz were much more aggressive in aiming fire at the race's leading candidate. Rubio in particular opened up new lines of attack on Trump, citing his previous employment of illegal immigrants, the foreign manufacture of his signature menswear, and the lawsuit in progress over "Trump University." Cruz mounted more familiar attacks on Trump from the ideological right, repeatedly portraying him as a phony conservative.
The change in approach reflected a new urgency in the Republican race, as the other candidates have suddenly realized that they can no longer wait for Trump to go away on his own. There is always risk in making attacks in a multi-candidate contest (John Kasich, who conspicuously declined to join in, obviously hopes to gain support from conflict-weary voters by remaining above the fray), but Cruz and Rubio have both concluded that Trump has become a serious threat to their candidacies. Though they may still view each other as one another's chief rival for votes, a Trump sweep over the next three delegate-rich weeks would put them both out of the running. At this stage, simply playing for time is a sensible strategy.
The collective joy expressed by the news media when Rubio went on the attack reveals the pent-up frustration within the political world with the lack of obstructions that have been placed between Trump and the nomination. But it will take more than one debate to derail Trump's candidacy. In fact, if both Rubio and Cruz turn out to benefit from the debate, the prospect that one of them will soon fold his campaign grows slightly dimmer, to Trump's strategic advantage. The race is by no means over, but the anti-Trump case will have to be made more forcefully—perhaps via some negative ads?—than it has so far.