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HOUSTON – Fearful that Donald J. Trump is irreparably damaging the conservative movement, Republican leadership is quietly planning a series of obstacles to place before the juggernaut presidential candidate that may result in a nomination fight on the floor of the party’s national convention in July.Anti-Trump Super PACs – independent political action committees – are aggressively staffing up, fund-raising and lobbying party elites to unite against Trump. They seek to suppress his rebellious voting bloc, if not convert its members, and to motivate anti-Trump primary voters not specifically toward one candidate or another, but into an anti-Trump bloc that prevents the New Yorker from sealing the requisite number of delegates for nomination.Put simply, they seek to divide pledged delegates to the nomination into two camps: The Trump camp and the not-Trump camp, preventing him from reaching the 1,237 delegates needed to clinch the nomination.GOP rules provide Trump with the nomination automatically should he reach that number. And if he continues to win with the margins he has secured in recent races – he has, thus far, won 10 of 15 contests – then he is on track for the nomination.But failure to reach that number prompts one of two scenarios. In the first, “super delegates” – party elites free to vote as they please – can support Trump, providing him with the number of delegates he needs to put him over the top. (But the Republicans have far fewer super delegates – three members of each state’s national party – than the Democrats.)The second scenario entails a truly brokered, or “open,” convention, in which a vote of all delegates fails to secure his nomination. In that second scenario, a fresh ballot frees previously pledged delegates from their state-assigned voting obligations. Candidates across the board – from underdogs to alsorans – may then lobby for their support.All 15 states that have voted thus far have allotted their delegates to the convention on a vote-proportionate basis, and Trump has won 285 of those delegates. But collectively, the other four candidates in the race have won 288.Those candidates are Sen. Ted Cruz of Texas, Sen. Marco Rubio of Florida, Gov. John Kasich of Ohio and neurosurgeon Ben Carson.The race now enters a riskier stage to those opposed to Trump, when major, delegate-rich states – including Florida, Illinois, Ohio, New York and California – award their prizes on a winner-take-all basis.Party leadership – including Senate Majority Leader Mitch McConnell and House Speaker Paul Ryan – is distancing itself from Trump, who Rubio said on Tuesday night threatened to destroy conservatism as we have come to know it.To break the front-runner’s momentum, Rubio, Cruz and the party establishment are planning a kitchen-sink assault. They will cast him as a wolf in sheep’s clothing, a con artist, an international embarrassment, a man without either Democratic or Republican principles.They will highlight his decision to start a sub-prime mortgage company six months before the 2008 financial crisis, his lifelong support for abortion and universal healthcare, his failed business ventures, a standing fraud lawsuit against him and his rumored connections to organized crime.But Trump, who has been in the public eye for three decades, has proven virtually immune to attack thus far. And while he may have high unfavorable numbers across the US, and a ceiling of support in his own party, neither of those factors particularly matter in his fight to secure the nomination.