Far from weakening Donald Trump, criticism by political rivals and pundits in the United States and even overseas appears to be even strengthening the Republican presidential front-runner in his quest for the White House.

The latest polls showing Trump further increasing his lead over his Republican presidential rivals appear indicative of this.

Moreover, a recent focus study on the people supporting Trump also bore this out. In the study, 29 people—20 men and nine women—who identified themselves as Trump supporters gathered in Alexandria, Virginia, on Wednesday night and were asked to rate their support to Trump on a scale of one to 10, the Los Angeles Times reported.

At the start of the study, 10 people said they were at nine or 10, noted David Merritt, managing director of Luntz Global, a political firm led by longtime Republican strategist Frank Luntz, who conducted the focus group study.

By the end of the night, the number of sure Trump voters rose to 16.

"His support is more intense than any candidate in this race and it's shown that in the polls," said Merritt. "We've found the more that he's criticised as a candidate, the stronger the support actually becomes."

On Trump's plan to bar Muslims from entering the U.S., 17 of the 29 participants said they supported the idea.

"Trump is the only one who would come out and say something like this. No one else can say it," said Tina Collier, 65. "You know what Trump does? He says something completely crazy and inflammatory, and then he dials back and explains it. To me he's whip-smart, he's a leader, he's going to do things other people haven't done."

Scott Mexic, a businessman, said that despite some of Trump's ideas, he still believes the business tycoon would make a good president.

"He says some things that are off-color," Mexic said. "But I still think he's a leader."

There is a possibility that the Republican Party could dump Trump even if he's the front-runner in the polls. If this happens, Trump said he will not rule out a possible run as an independent should he fail to secure the Republican nomination.

"If [Republicans] don't treat me as the front-runner ... if the playing field is not level, then certainly all options are open," Trump told CNN on Wednesday.

Many in the Virginia focus group said they would back Trump even as an independent candidate.

Meanwhile, a new poll showed that although a majority of U.S. adults oppose Trump's plan to ban all Muslims from entering the country, Republican primary voters are split evenly.

Trump's proposal is opposed by 57 percent of American adults and supported by 25 percent, an NBC News/Wall Street Journal survey released Thursday shows.

However, Trump's proposal is agreeable to half of the Republicans who are likely to vote in the 2016 presidential primary—38 percent support Trump's proposal, while 39 percent oppose it.

Among adults who identify as Republicans even if they might not vote in the primary, 42 percent support Trump's plan, while 36 percent oppose it.

In sharp contrast, 75 percent of Democrats and 55 percent of independents oppose Trump's call to bar Muslims from entering the U.S.