By Steve Holland

ORLANDO, Fla. (Reuters) - U.S. Republican presidential nominee Donald Trump's campaign team is to meet officials from the Republican National Committee on Friday in what both groups described as a routine session to discuss joint operations in Florida.

Trump, who is lagging Democratic nominee Hillary Clinton in opinion polls, was not expected to attend the Orlando gathering after staging a rally near there on Thursday. He is to hold separate events on Friday in Erie and Altoona, Pennsylvania.

The New York businessman is struggling to get past a rough several days, when he suggested gun rights activists could take action against Clinton, a statement he later said was aimed at rallying votes against her.

In recent weeks, a steady stream of moderate Republicans, such as U.S. Senator Susan Collins of Maine, have vowed not to support Trump, while 50 Republican national security experts signed a letter opposing him.

Many Republicans not only worry about failing to win the White House, but also are alarmed that their majorities in the Senate and House of Representatives could be at risk.

Trump has blamed the U.S. news media for taking many of his comments out of context, and on Thursday night, some of his supporters heckled and cursed reporters who covered the rally in a large arena in Kissimmee.

On Friday, Trump passed off as sarcasm the assertion he made repeatedly this week that President Barack Obama and Clinton were "co-founders" of Islamic State and its Most Valuable Players.

"Ratings challenged @CNN reports so seriously that I call President Obama (and Clinton) 'the founder' of ISIS, & MVP. THEY DON'T GET SARCASM?" Trump said in a tweet.

It was the second time in recent weeks that Trump has explained a controversial statement as sarcastic. In late July, he invited Russia to dig up tens of thousands of "missing" emails from Clinton's time as U.S. secretary of state, which raised concerns among intelligence experts that he was urging a foreign government to spy on Americans.

He said later he was being sarcastic.

(Reporting by Steve Holland; Editing by Richard Pullin and Lisa Von Ahn)