Democratic vice presidential nominee Tim Kaine on Tuesday questioned whether Donald Trump is healthy enough to be the next president, a line of inquiry that comes as Democrats decry those who raise similar concerns about Hillary Clinton.

Voters want and deserve to know if candidates are in "good enough health to perform their duties," Kaine said at a campaign stop in Erie, Pa.

"We've never had a candidate quite like Donald Trump. He has no comparable public record, and so we know less about him than we know about other candidates in modern history. And that makes these questions … about his health even more urgent than usual," he said.

The Virginia senator added, "Donald Trump thus far has utterly failed to answer basic questions that American voters have a right to know."

Kaine's remarks come as Trump and his supporters continue to raise questions about whether Clinton is healthy enough to take over as commander in chief.

As the GOP nominee has hinted repeatedly at her supposedly poor health by claiming she doesn't have the energy and stamina to lead, his allies in right-wing media have followed suit. Some in online media have even theorized that Clinton is in engaged in some sort of elaborate cover up, including that she wears excessively baggy clothing so as to conceal the bulge of bulky medical devices.

Clinton's campaign has pushed back on claims her physical health is deteriorating rapidly, and her team has characterized claims to the contrary as "conspiracy theories."

"For some reason, recently, Donald Trump started to trade in Internet conspiracy theories from the fringes of the Internet suggesting that Hillary Clinton is in poor health," Kaine said Tuesday.

The vice presidential candidate added, "I have been on the trail with Hillary for five weeks and I can barely keep up with her. I have been on the ticket for five weeks, and she has been running on full speed for 17 months. I can tell 'ya, Hillary Clinton is one tough and one healthy person."

Clinton's communication director, Jennifer Palmieri, echoed these sentiments in a statement released earlier this month to Politico

"While it is dismaying to see the Republican nominee for president push deranged conspiracy theories in a foreign policy speech, it's no longer surprising," she said.

Clinton's personal physician, Dr. Lisa Bardack, has also released a statement saying documents supposedly showing Clinton is in poor shape aren't accurate.

"As Secretary Clinton's long time physician, I released a medical statement during the campaign indicating that she is in excellent health," she said.

For Trump's part, the only medical record that he has made publicly available is a hastily written letter claiming he would "be the healthiest individual ever elected to the presidency."

"I don't think he's in any better or worse (shape) than the average person that goes and exercises every single day," Trump's physician, Harold Bornstein, told NBC News last week. "Doesn't smoke, doesn't drink — and that's simply the best advantage you can have to live — and he's got a good family history."

Trump has said he'd release more information if Clinton releases additional medical documents. Her campaign has dismissed this challenge, saying that the Republican candidate has failed to come close to matching the level of information that Clinton has already made publicly available.

"From hiding his tax returns and the extent of his debt laden conflicts of interests with foreign interests to the laughable 'medical record' that was literally written in five minutes, Donald Trump is making a mockery of transparency," said Clinton spokesman Glen Caplin. "We know the least about Donald Trump of any candidate in recent memory."

"While Trump and his allies push conspiracy theories designed to delegitimize her personally, we will continue to go on offense and call out the truly destructive theories calmly, but aggressively, and in real time," he said.

Kaine added his own thoughts Tuesday.

"Here's the bottom line: Hillary Clinton has met every test of disclosure we expect of presidential candidates, and in many cases has gone on even further," he said. "Donald Trump has failed all these tests miserably."

"The Trump campaign just feels like Trump's next big con," Kaine said.