TAMPA, Fla. — For more than a year, the 2012 campaign has featured two Republican Parties: the official one of candidates, party leaders and elected lawmakers, and the unofficial one of “super PACs” and other outside groups raising and spending tens of millions of dollars to help the Republicans win in November.

But over four days here, those two parties have all but merged into a unified conservative machine, working inside and outside the system, mixing establishment and grass roots, abiding by campaign laws but also displaying just how flimsy the barriers between them are.

Supporters of Mitt Romney shuttled between briefings and receptions held by outside groups and events staged by his campaign near the site of the Republican National Convention, far less worried than they were a few months ago about the seldom-enforced rules barring coordination of activities between the official and unofficial sides. Top party officials appeared at forums sponsored by the network of tax-exempt groups that have helped them outspend President Obama and the Democrats. And the emerging class of megadonors fueling the shadow party and the official one shed their habitual reticence to be honored at receptions and galas.

In a St. Petersburg penthouse overlooking Tampa Bay, Mel Sembler, an ambassador in the George W. Bush administration who is a Florida finance chairman for Mr. Romney, hosted a reception on Wednesday for Restore Our Future, the super PAC that intends to spend more than $100 million to help Mr. Romney win the White House. The invited speakers included several of Mr. Romney’s top surrogates on the campaign trail: Gov. Nikki R. Haley of South Carolina, Senator John Thune of South Dakota and Representative Jason Chaffetz of Utah.