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."
They have chosen to use fiscal 2017 reconciliation for Obamacare, then the fiscal 2018 process for tax reform.
"Before we do the tax — which is actually very well finalized — but we can't submit it until the health care statutorily or otherwise," President Donald Trump told reporters late last month before a White House budget meeting.
Both Obamacare repeal and tax reform were key Trump campaign promises. The president and GOP congressional leaders say an overhaul of the tax system will help to unlock economic growth and encourage companies to stay in the United States.
Trump's pledges to trim taxes for businesses and slash regulations, in particular, have helped to power a strong stock market performance since his election in November.
Republicans introduced a bill to replace the ACA this week, the American Health Care Act, and have moved quickly to pass it into law, with Trump's support. Both conservative and moderate pockets of the GOP have criticized parts of the plan, on top of staunch Democratic opposition, threatening to slow the process and derail Trump's broader agenda.