He also said there would be no government shutdown, despite attempts by conservatives to tie an effort to block funding for the women's health organization Planned Parenthood to any spending bill.
Despite McConnell's tough talk on Iran, it is Democrats who are poised to be decisive in the vote on the deal that comes in mid-September, and a key Democratic senator came out in favor of the deal Thursday.
New York Sen. Kirsten Gillibrand posted a piece on Medium titled "Why I'm Supporting an Imperfect Iran Deal," in which she wrote that "If we reject this deal, we do not have a viable alternative for preventing Iran from obtaining nuclear weapons."
Another Senate Democrat, Jeanne Shaheen of New Hampshire, expressed a similar sentiment in announcing her support later Thursday.
Still, Republicans plan to continue working against the agreement.
In his remarks to the media Thursday, McConnell blasted President Barack Obama's tough rhetoric on the Iran deal, which the President has said is the only option to avoid war with the country.
"That's an absurd argument, and it's the one they've made from the very beginning, that it's either what the President negotiates with the Iranians or it's war," McConnell said. "That's never been the alternative."
"Let me suggest that had the President and his team spent as much time trying to ratchet up the sanctions on the Iranians over the last two years as they have entering into an agreement, which most of us are highly skeptical of as to having any positive impact at all, we'd have ended up in better place," he said.
McConnell said Obama was treating the Iran deal sales effort like a political campaign rather than a serious national security debate and argued that while the President said the agreement with Iran would "completely transform the Middle East," those changes would not be for the better.
"It has the potential to transform the Middle East alright, but it strikes me not into a safer Middle East, but one more racked with discord," the Kentucky senator said.
Iran is the first order of business after the August recess and Congress is in the midst of a 60-day review of the nuclear deal reached with the country. It must vote on whether to approve or disapprove of the deal by Sept. 17. The vast majority of Republicans oppose the deal and a resolution of disapproval is expected to pass both chambers.
Obama is expected to veto that resolution, and the White House is hoping to persuade enough Democrats to back the deal to help sustain his veto. House Speaker John Boehner said recently Republicans would "to do everything possible to stop" the agreement. McConnell told reporters Thursday he did not want to "handicap" the outcome of efforts to halt the deal.
Congress is also facing a deadline on funding the government. Legislation to do so must be passed by Sept. 30 to avoid a shutdown. Boehner said last month Congress would have to pass a short-term funding bill to avoid a shutdown, given the calendar crunch after the recess and ongoing disputes over funding bills.
On Thursday, McConnell acknowledged the importance of dealing with Planned Parenthood, citing ongoing investigations of the group by Senate committee, while also vowing to avoid a shutdown.
"We've been down this path before. This is a tactic that's been tried going back to the '90s frequently by Republican majorities and it always had the same ending: that the focus is on the fact that the government is shut down, not on what the underlying issue that is being protested is," McConnell said, adding later, "I can tell you without fear of contradiction there will be no government shutdown."
He did not explain how Congress would avoid a shutdown in the face of efforts to block spending bills, saying only that while it is easy for individual senators to gum up the works in the chamber through the use of procedural tools, the body had been able to surmount such challenges all year long.
The majority leader declined to weigh in on Thursday night's much anticipated match up among the top 10 Republican presidential hopefuls vying for the party's nomination. He ignored questions about what advice he would give to candidates facing off against the unpredictable and admittedly unrehearsed frontrunner Donald Trump, and about what he wanted to see in the debate.
"I'm hoping to see a two-hour debate," was all he would say.
McConnell spoke on the 50th anniversary of President Lyndon B. Johnson's signing of the landmark Voting Rights Act, which guaranteed the right to vote for people of all races after years of rampant discrimination, especially in the South. In 2013, the Supreme Court overturned a key provision of the law that required certain states with a history of racial discrimination at the polls to "pre-clear" any changes to the voting laws with the federal government before implementing them.
Democrats say states have taken advantage of that ruling to implement new restrictions they say make it harder for minorities, students, the elderly and others to vote. They have pushed Congress to pass an update to the act, but several pieces of legislation to strengthen the law have stalled on Capitol Hill.
The majority leader, who happened to be in the Capitol rotunda on Aug. 6, 1965, for the signing of that bill, reminisced about that moment, while also indicating he did not believe the law needed to be updated.
"It's been a big success. It's worked. The Supreme Court, of course, did not strike down the Voting Rights Act," he said. "I think it is also important to understand how different the South is now. Haley Barbour, he used to be governor of Mississippi, always pointed out there are more African-American elected officials in Mississippi than any other state in America. America's come a long way, and the Voting Rights Act is intact. It was not struck down."