Sen. Flake: Concerns need to be addressed before tax reform 7:05 PM ET Thu, 9 March 2017 | 03:24

Mitch McConnell thinks getting tax reform done, along with repealing Obamacare, could take longer than the Trump administration claims.

Politico on Thursday asked the Republican Senate majority leader if he thinks tax reform can be completed by August.

"I think finishing on tax reform will take longer. But we do have to finish the health-care debate, up or down, win or lose, before we go to taxes," McConnell told Politico.

Treasury Secretary Steven Mnuchin previously told CNBC he wanted to see "very significant" tax reform passed by Congress' August recess. Asked Thursday if he could give a more realistic timeline for a tax overhaul, McConnell said, "I don't know. It is complicated."

Republicans have started a packed legislative calendar by pushing to repeal and replace the Affordable Care Act, also known as Obamacare. For both political and procedural reasons, the GOP aims to pass health-care reform first, then turn to tax reform.

Later Thursday, White House press secretary Sean Spicer insisted that Trump plans to stick to the schedule the administration detailed previously.

"I think we feel confident that we're going to get a lot done, continue to get a lot done this year," he said.

Republicans have two chances for a procedure called budget reconciliation, which requires only a Senate majority and can bypass Democratic opposition. McConnell said "we know (Democratic senators are) not going to participate."