Donald Trump faces a herculean task to win over party critics. (File Photo)

Bombastic mogul Donald Trump will cap his improbable takeover of the Republican party at a convention in Cleveland starting Monday that promises to be contentious and decidedly unconventional.The former Democrat and political neophyte is poised to formally secure the White House nomination for the Party of Lincoln after a thumping primary win.The quadrennial rally is designed to bring Republicans together, formally select a presidential nominee and catapult the party towards November's election.But Trump faces a herculean task to win over party critics.His salty rhetoric and populist message has outraged conservatives and sparked a battle for the soul of the Republican party.For many, this is a hostile takeover."I reject Donald Trump as our party leader," vanquished Republican rival Jeb Bush said as delegates headed to Cleveland.Conspicuously, the four day political jamboree will feature no former presidents, few party luminaries and only a smattering of elected officials.George W. Bush, John McCain and Mitt Romney, the last three Republican presidential nominees, are staying well away.Trump will depend instead on his running mate, Indiana Governor Mike Pence, and his family- wife Melania, daughters Ivanka and Tiffany and son Donald Trump Jr.- to make his case.Uncharted TerritoryAfter months of rocky sailing, the controversial businessman had seemed to be heading into the convention with the wind at his back.National polls show him tied with Hillary Clinton, who has been buffeted by an email scandal that led the FBI to call her "extremely careless."Some skeptics have been assuaged by the selection of Pence, a bonafide conservative from a state which the Democrats won in 2008."Governor Pence strengthens the ticket with a solid and unquestionable conservative anchor," Maureen Blum, a convention delegate from Washington who backed Trump rival Marco Rubio, told news agency AFP.But as the convention nears Trump is again in choppier waters.His apparent dithering over a "final, final" decision on a Pence could badly undercut his image as a decisive leader.Trump had scheduled his VP's unveiling for Friday, then cancelled it- citing the attacks in Nice- before finally going ahead.The roll out of the announcement had also raised serious questions about his campaign's competence.Pence is virtually unknown in most of the country, but the Trump campaign appeared to make no effort to define him to voters.Instead that job was left to Hillary Clinton's campaign, which within minutes had unleashed a barrage of emails, texts, videos and social media posts describing Pence as anti-women and anti-gay."Pence is the most extreme pick in a generation," said Clinton campaign John Podesta.Internal UnrestThere was some good news for Trump when it emerged that last-ditch efforts by his opponents to change party nominating rules and thwart his candidacy failed.But that has led to little sign of reconciliation."#NeverTrump is never more. They were crushed last night in Cleveland at Rules Committee by a vote of 87-12. MAKE AMERICA GREAT AGAIN!" Trump tweeted.That uncompromising tone and lack of magnanimity is unlikely to win him new friends."I want to vote for a Republican nominee, I absolutely do," first-time Texas delegate Laura Koerner told AFP."But I also want to feel confident that I'm voting for a person who represents my values.""I don't think he is the best candidate for the Republican party."Even delegates like Koerner who are willing to give Trump a chance want to see a dramatic change in tone at the convention."I want his level of political discourse to go up, not down," Wayne Bena, a Nebraska delegate who prides himself on remaining neutral, told AFP."I want to see a positive message, I want us to speak positively about our country and the campaign, and not tear the other person down."Republican officials have promised the convention's theme will be the same as that of Trump's campaign: a pledge to "Make America Great Again."Topics to be covered are "national security, immigration, trade and jobs" according to Jeff Larson, CEO of the 2016 Republican National Convention.Against the backdrop of attacks in San Bernardino, Brussels, Orlando, Nice and turmoil in the Middle East, Trump may continue to bet on a tough tone and tactics that have got him this far.