Donald Trump is set to make his case to America - and to the many rattled doubters within his own party.
The most important speech of his presidential campaign so far will bring down the balloons at a Republican convention marked by divided loyalties and unwanted distractions.
Competing passions were sharply on display on Wednesday night when Mr Trump's fiercest primary rival, Ted Cruz, stopped far short of endorsing the nominee and drew loud boos from the audience.
The remarkable scenes overshadowed the speech by Mike Pence, who was formally nominated for vice-president.
Mr Cruz was defeated by Mr Trump in the race to become the Republican candidate, and in his speech to party delegates he mentioned the tycoon by name only once, and stubbornly refused to endorse him as he encouraged Americans to simply "vote your conscience" in November.
Mr Trump unexpectedly walked into the arena just as Mr Cruz was ending his remarks. Delegates chanted Mr Trump's name and implored Mr Cruz to voice his support for the businessman, to no avail.
Mr Cruz's wife Heidi even had to be escorted from the convention floor for her own safety as she was heckled by Trump delegates.
Mr Trump later tweeted about Mr Cruz's speech: "No big deal!" He said he saw the text of his speech two hours before it was delivered but thought "let him speak anyway".
The extraordinary scenes on Wednesday night show how split Republicans are following Mr Trump's controversial campaign, and were at odds with the later claim by Mr Pence that it is a "united party".
Mr Trump's top adviser said Mr Cruz "used very bad judgment" when he failed to endorse the presidential nominee.
Paul Manafort told NBC's Today on Thursday morning that Mr Trump invited his primary opponents to address the convention in Cleveland because "he views the primary process as over". Convention delegates formally nominated Mr Trump on Tuesday.
Mr Manafort added that Mr Cruz "was not respectful" to that invitation, but he insisted despite that snub, the Republican Party is coming together.
Mr Trump will close the convention with his speech on Thursday evening.