Donald Trump has lamented that New York bombing suspect Ahmad Khan Rahami would receive medical treatment and legal representation after his arrest.
The Afghan-born, 28-year-old was charged with five counts of attempted murder after a police shootout.
The Republican nominee said it was a "sad situation" and underscores the country's weak national security.
Meanwhile, Democratic rival Hillary Clinton said Mr Trump's rhetoric only helped terrorist groups.
"The kinds of rhetoric and language that Mr Trump has used is giving aid and comfort to our adversaries," Mrs Clinton told reporters at a news conference outside New York City.
She added that she was the only candidate equipped with the experience of being "part of the hard decisions to take terrorists off the battlefield".
Mrs Clinton also pledged to build trust between law enforcement and Muslim-American communities.
Mr Trump fired back in a statement, saying that a Clinton presidency would only lead to "more attacks on our homeland and more innocent Americans being hurt and killed".
Later at a campaign rally in Fort Myers, Florida, Mr Trump decried Mr Rahami's treatment for gunshot wounds and legal representation, which is his constitutional right under the Fifth Amendment.
"But the bad part, now we will give him amazing hospitalisation. He will be taken care of by some of the best doctors in the world," Mr Trump said.
"He will be given a fully modern and updated hospital room. And he'll probably even have room service knowing the way our country is."
He suggested that any punishment would be too lenient on Mr Rahami, who has yet to be charged in connection to the New York and New Jersey bombings.
"His case will go through the various court systems for years. And in the end, people will forget, and his punishment won't be what it once would have been," Mr Trump said. "What a sad situation."
He repeated calls for "extreme vetting," which would include an assessment of whether potential immigrants share American values.