For months, Republican senators Ted Cruz and Marco Rubio have thrown sharp elbows, traded insults and compiled thick files on one another in anticipation of the moment they would find themselves in a knockout fight for a showdown with Donald Trump.
That moment has arrived.
In South Carolina's primary, Rubio held a slight lead over Cruz in their battle for second place behind Trump after one of the nastiest weeks of their bitter rivalry. The two young Cuban American senators are effectively in a three-man race and raising the stakes in their one-on-one battle.
Rubio will now look to consolidate the mainstream wing of the Republican Party, which is already beginning to line up behind him and will likely continue to after Jeb Bush's departure from the race. His playbook against Cruz is to cast his Texas colleague as dishonest and assail his record on national security as weak and contrast that with his sunnier "new American century" message.
"After tonight, this has become a three-person race, and we will win," said Rubio in a speech to supporters.
In his speech, Rubio commended Bush and praised him for "running a campaign based on ideas". Cruz lauded Bush for bringing "honour and dignity" to the race.
Cruz told supporters he is the only candidate who can take on Trump. "This is the only campaign that has beaten, and can beat, Donald Trump," said the senator, who edged Trump in the Iowa caucuses.
Cruz is aiming for a strong showing in a slate of Southern states on March 2. His anti-Rubio scheme: Present the Floridian as a centrist masquerading as a conservative on a range of issues.
The Cruz-Rubio struggle will pitch quickly to Nevada, where Rubio and Cruz plan to campaign hard ahead of Wednesday's caucuses.
Beyond Nevada, Cruz hopes to do well in the collection of Southern states that will vote on March 2.
Cruz has said the South could prove to be a "firewall" for his campaign, which has spent months pouring resources into the delegate-rich region.
Rubio stands to gain the most of any candidate from Bush's exit from the campaign. Many in Bush's deep donor pool are expected to think seriously about supporting Rubio now.
John Kasich has signalled he plans to stick around, eyeing March contests in Midwestern states such as Michigan and his home state of Ohio. If he does, that would be a blow to Rubio.
Rubio strategists are trying to stay within shouting distance of Trump in the states leading up to March 16, when most states will begin to allocate their delegates on a winner-take-all basis. His aides believe a winnowed field will redirect more support to him than to either Trump or Cruz.
At Cruz's watch party, a cheer went up when Bush announced he was suspending his campaign. The same thing happened at Rubio headquarters.
The real estate mogul has now won two out of the first three states to vote and is very likely to cruise in Nevada's caucuses. Trump is also ahead in virtually every one of the 13 states set to vote March 2. There can be no doubt now: Donald Trump is the favourite to be the Republican nominee for president.
The Florida senator got a clear signal that he is the establishment candidate who can win. Rubio should be well positioned to do well in Nevada - a showing that will solidify him as the clear alternative to Trump.
The South Carolina electorate was ready-made for the Texas senator: heavily evangelical and very conservative. Cruz isn't winning enough of the evangelical vote, and he can't win votes outside the evangelical community.
The South Carolina Governor jumped into the race for Rubio and can now claim she helped him to second place. (Yes, I know that seven in 10 Republicans said the endorsement didn't make their mind up. People never say that someone else influences their vote; we're too proud.) Haley allowed Rubio to cast himself as part of the new face of the party, a powerful message. If he winds up as the nominee, Haley will be first among equals to be his vice-presidential pick.
- Washington Post, Bloomberg