"I do think it's a good idea for the American voters to take a look at the system that we have," the Iowa Republican and Trump supporter told CNN's Chris Cuomo on "New Day." "There is significant evidence out there that there is voter fraud."
While King agreed with Trump's claim of significant vote fraud, which lacks evidence, he also said it shouldn't be the candidate's chief talking point.
"I think there is truth to some of the things that he lays out on this, I just don't think it's that constructive to make it the campaign issue," King said.
"This is something we'd agree on, Democrats and Republicans. The Constitution is the foundation of our country, but the bedrock that it sits on is legitimate free and fair elections, and the public has to perceive that they are free and fair," King added. "And I do think there is concern here that there are voices out there to de-legitimize this election."
Trump and his surrogates, including Rudy Giuliani, are continuing to repeat their argument that elections can be rigged, while some top Republicans, including vice presidential nominee Mike Pence, are saying they trust the political system and will accept the results on Election Day.
Top Republicans are concerned more talk of rigged elections could lead to unrest during an after Election Day.
Ohio Secretary of State Jon Husted, a Republican who says he is voting for Trump, pushed back against Trump's claim and sought to reassure voters on CNN Monday.
"We have so many safeguards in place in our election system. It's bipartisan, it's transparent, and there's just no justification for concern about widespread voter fraud," Husted said.
"He should focus on trying to reach people, and give them hope that he can be a leader that will ultimately move America forward," Husted said. "This kind of conversation moves America backwards and it should be dismissed."
Last week, a Trump supporter told Pence
if Clinton were elected she would be "ready for a revolution," to which Pence responded "don't say that."
And Trump tweeted
Monday, "Of course there is large scale voter fraud happening on and before election day. Why do Republican leaders deny what is going on? So naive!"