"Every meeting I have, everywhere, people are asking what is happening with the United States, 'What are you doing to yourselves?' " the 2004 Democratic presidential nominee said Tuesday on MSNBC's "Morning Joe."
"But in the end, I am confident that the American people are going to choose wisely," Kerry said.
President Barack Obama seconded Kerry's sentiment in remarks Tuesday, saying foreign impressions of the GOP race were damaging the United States' reputation.
"I'm getting questions constantly from foreign leaders about some of the wackier suggestions that are being made," Obama said during an appearance in the White House briefing room. "I have to emphasize that it's not just (Donald) Trump's proposals. You are also hearing concerns about (Texas Sen. Ted) Cruz's proposals, which in some ways are just as draconian when it comes to immigration."
Later, White House Press Secretary Josh Earnest said the damage has come in the form of less productive meetings with foreign leaders, who are intent on hearing Obama or Kerry explain the political battle.
Trump, the GOP front-runner, drew international attention last week when he suggested Japan should arm itself
to deter a threat from North Korea rather than have the U.S. military protect the longtime ally against the rogue nuclear nation.
Trump has also maintained that the U.S. should pressure NATO member states to begin "paying their fair share."
"I would rather have them not arm, but I'm not going to continue to lose this tremendous amount of money. And frankly, the case could be made that let them protect themselves against North Korea. They'd probably wipe them out pretty quick," Trump said in Wisconsin.
The business mogul turned politician also called NATO "obsolete" and said member states "should start paying their fair share."
Trump has also voiced some of the strongest criticism
against the Iran nuclear deal, which Kerry helped broker.
The Republican front-runner dominates national polls
, while Democratic candidate Hillary Clinton continues to lead rival Bernie Sanders on the other side.