Washington (CNN) Donald Trump says has no worries about the next GOP presidential debate, although he expects his fellow candidates to come after him.

And one of those candidates, Rand Paul, found himself the target of Trump's latest Twitter salvo Saturday afternoon.

The remarks began when Trump was asked after a campaign event in Boone, Iowa, how he was preparing for next Wednesday's debate.

"My whole life is preparation for a debate," the mogul said.

Trump added that he wasn't worried about being onstage with Carly Fiorina. The former technology executive made the top-tier debate stage in a late amendment to the rules for Wednesday's CNN debate that accounted for her surge in the polls.

An interview with Trump published this week quoted him as insulting her appearance , though he later said he was referring to her persona. But Trump said he's not concerned about her joining him in the top-tier debate.

"I think she's a very nice woman. I'm not at all (worried)," Trump said in Iowa. "I think she'll do well -- I asked that she be on the debate because I think she should. I think 11 people are far too many, but that'll start weeding out."

But Trump also told reporters he expects some of his opponents to go on the attack during the debate -- and used it as an opportunity to put some of them down.

"I'll be attacked," Trump said. "Somebody will attack, you know, somebody like a Rand Paul who's down at about 2%. ... He's been very nasty lately."

Trump said Paul was nice to him until "all of a sudden about a week ago he starts attacking because his poll numbers are down."

"He's a very ineffective guy," Trump said. "Rand is weak on immigration. He's weak on the military. He's got no chance; he's down so low with his polls, he's got no chance."

Paul has long been referring to Trump as a "fake conservative" on the trail and said in Iowa this weekend that it's time to take Trump on, according to Radio Iowa

Trump predicted that would be a bad strategy, saying attacking him has been harmful for candidates, including former Texas Gov. Rick Perry, who dropped out of the race Friday; South Carolina Sen. Lindsey Graham, who Trump said was "down to almost zero"; and former Florida Gov. Jeb Bush, who's recently lost ground in the polls.

"It certainly seems to be unlucky to attack me," Trump said.

But Trump wasn't done. He soon went on Twitter after the event to taunt the Kentucky senator.

"I truly understood the appeal of Ron Paul, but his son, @RandPaul, didn't get the right gene," he tweeted. He added: "Lightweight Senator @RandPaul should focus on trying to get elected in Kentucky--- a great state which is embarrassed by him."

Tweeting further: "Too many people on stage for debate. @RandPaul at 11th, with 2% in @RealClearNews, shouldn't be allowed to participate."

I truly understood the appeal of Ron Paul, but his son, @RandPaul, didn't get the right gene. — Donald J. Trump (@realDonaldTrump) September 12, 2015

Lightweight Senator @RandPaul should focus on trying to get elected in Kentucky--- a great state which is embarrassed by him. — Donald J. Trump (@realDonaldTrump) September 12, 2015