Washington: Six years after a Supreme Court decision opened vast new channels for money to flow into national elections, Democrats have built the largest and best-coordinated apparatus of outside groups operating in the 2016 presidential campaign, defying expectations that conservative and corporate wealth would dominate the race.

A dozen organisations raised more than $200 million (Dh734 million) through the beginning of October and since May have spent more than $110 million on television, digital and radio ads in support of Hillary Clinton, according to records filed with the Federal Election Commission through Thursday.

The handful of organisations backing Donald Trump have raised less than half that amount, a steep dive from four years ago, when wealthy Republicans poured hundreds of millions of dollars into groups backing Republican nominee Mitt Romney.

The Democrats’ success this year reflects, in part, Clinton’s close personal ties to her party’s elite donors and her allies’ willingness to exploit the 2010 ruling in the Citizens United case far more aggressively than US President Barack Obama did.

But the Democrats are also deeply indebted to one man: Trump, whose provocations and tirades — along with a loud crusade against his own party’s donors — have virtually shut off what once promised to be a half-billion dollar spigot of outside money.

“Everyone thought that we would be outspent, that there would be significant operations built at the presidential level for the other candidate,” said Guy Cecil, a former Clinton aide who heads Priorities USA Action, the main hub of big Democratic giving. “That obviously hasn’t happened.”

The biggest groups set up or expanded by conservatives since Citizens United, including American Crossroads, founded by Karl Rove, and the network overseen by Charles G. and David H. Koch, are absent from the presidential campaign, focusing instead on protecting Republicans in Congress.

“Unlike President Obama four years ago, Clinton embraced the outside money game and shrewdly empowered a single group to carry her message,” said Steven J. Law, president of American Crossroads and its sister organisations, “in contrast to the boardwalk arcade of groups supporting Trump.”

Citizens United paved the way for independent groups that could raise unlimited amounts of money from unions, corporations and wealthy individuals to spend on elections, as long as they did not coordinate with individual candidates or parties. Republican donors moved quickly to seize on the ruling, pouring hundreds of millions of dollars into the last three national elections, while Democrats struggled to persuade their donors to invest in super political action committees (PACs) on the same scale.

Trump’s rivals for the Republican nomination were backed by an array of super PACs and outside groups set up by their allies and former aides, seeming to set the stage for even greater spending in 2016. But Trump unexpectedly triumphed, exploiting his knack for free publicity and relying on his own fortune and money from grass-roots supporters. In part because of that success, Trump was slow to incorporate super PACs into his general election strategy.

By contrast, Clinton began personally courting donors for outside groups almost as soon as she entered the campaign in spring 2015.

The Democrats’ tentpole is Priorities USA, a five-year-old super PAC that has access to the party’s biggest donors and the implicit blessing of Clinton, is on track to raise $173 million by Election Day. That is more than any equivalent Democratic effort in history, including the controversial big-money groups set up by wealthy liberals a decade ago to unseat President George W. Bush.

The PAC is closely coordinating with environmental and labour activists and other organisations set up to harness support from veterans, African-Americans and Latinos.

In twice-monthly meetings at a Democratic law firm in downtown Washington, officials at Priorities have convened representatives of a dozen super PACs and progressive organisations to carve out swing-state turf and share intelligence from organisers on the ground. Several have pooled money with Priorities USA to purchase television and digital advertising through the same media firms, allowing smaller groups to get better rates. (Other left-leaning organisations, including labour unions and a super PAC founded by billionaire environmentalist Tom Steyer, have separately spent significant money on field organising.)