The people who are vehemently opposed to a Donald Trump presidency made a show of force over the weekend, blocking traffic near a Trump event in Arizona, marching to the Trump Tower in New York City, and even issuing threatening letters to the Republican presidential front-runner's family members.

The protesters in Arizona parked vehicles sideways on Shea Boulevard, blocking both lanes of traffic into Fountain Hills, where Trump held a rally on Saturday afternoon, CNN reported.

On Friday night, the protesters tried to barge into the venue of a Trump rally in Salt Lake City, Utah, forcing the police and Secret Service officers to abruptly close the doors as Trump was speaking. Last week, scuffles broke out between protesters and Trump supporters in Chicago that led to the cancellation of a rally there.

During Friday night's rally, Trump once again talked about bringing jobs back to the U.S. from overseas, imposing tariffs on products made in Mexico and blasting President Barack Obama's foreign policy. But his main focus was on illegal immigration, a major issue in Arizona.

"So much crime. Drugs pouring though the border. People are now seeing it. And you know what? We're going to build the wall and we're going to stop it. It's going to end," Trump said. "Unless you have a border, you don't have a country. Remember that."

While he was speaking in Tucson later Saturday, dozens of protesters crowded outside the Tucson Convention Center, chanting, "No more hate" and "Trump the racist."

Trump was repeatedly interrupted by protesters, some of whom clashed with his supporters. At one point, Trump remarked, "These are not good people folks. They're not really protesters, they're agitators."

While the protest in Arizona was going on, demonstrators gathered in New York City, Trump's hometown. Brief clashes took place when protesters threw water bottles at police, who were trying to keep them from impeding traffic. Three people were arrested and charged with disorderly conduct, a New York police spokesman said.

Meanwhile, Trump's older sister, federal appeals court judge Maryanne Trump Barry, was reported to have received a threatening letter in Philadelphia on Friday — one day after Trump's son received a suspicious piece of mail containing white powder.

There was no white powder sent to Trump Barry, although the threat included in her letter was similar to that given to Eric Trump, a source familiar with the investigation told NBC News.

The letter Eric Trump received on Thursday demanded that his father drop out of the Republican race for the presidential nomination.

In a bid to ease rising tension in the Republican Party, Trump has decided to meet on Monday with nearly two dozen top Republicans for the first time in an off-the-record session, Newsmax reported.

"Mr. Trump is continuing his outreach to Washington and there has been an overwhelming positive response," Trump campaign manager Corey Lewandowski said.

The session will be held before the Republican front-runner speaks to the American Israel Public Affairs Committee in Washington, Lewandowski said. He would not say who would be attending.

The meeting was arranged by Alabama GOP Sen. Jeff Sessions, whom Trump named head of his foreign policy advisory committee this week, the Washington Post reported.