"The first thing I'd do in my first day as president is close up our borders so that illegal immigrants cannot come into our country," Trump said in a Twitter question and answer session from Twitter's New York office. "People can come into our country, but only legally. I will close up those borders," added Trump in his video answer, returning to an issue that accompanied his initial jump to the top of polls. .@MarieLeff #asktrump pic.twitter.com/ufCLFKeFrN — Donald J. Trump (@realDonaldTrump) September 21, 2015 Using the #AskTrump hashtag, the real-estate tycoon fielded questions about NFL players, Israel and guns, among other topics.

Trump, who has dominated the GOP field for weeks, remains the front-runner but has fallen 8 percentage points since earlier this month, according to a CNN/ORC International poll released Sunday.

On Monday, Trump followed other presidential candidates, such as Hillary Clinton, who have answered questions on social media in an attempt to gin up online interest and interaction.

Trump said in the first of a dozen short videos that were part of his Twitter Q-and-A that he would "totally protect Israel" if elected president.

He also offered advice on being a successful businessperson, said he would "take care" of homelessness by focusing on jobs and tackle healthcare affordability as president.

The responses also involved lighter topics, such as Dallas Cowboys quarterback Tony Romo leaving Sunday's game against the Philadelphia Eagles with a fractured collarbone. "The fact that Tony Romo got hurt is a terrible thing for the Dallas Cowboys," Trump said in one of his first responses. "I think Tony is a great guy — I know him — and he's also a great football player. And it will certainly hurt Dallas. But their defense is excellent."