BY MICHAEL TANNER

When President Donald Trump is sworn, Republicans will hold the presidency and both houses of Congress for the first time since 2006. For everyone who has been complaining about gridlock for the past decade, there is now the possibility of action.

But before everyone joins hands and sings “Kumbaya,” it’s worth noting that President Trump and Republicans in Congress don’t exactly see eye-to-eye on a host of issues.

Of course, Republicans will have every incentive to deliver some quick victories. Even those who didn’t support or don’t like President Trump have a vested interest in his success. And, certainly, they will be chastened by the grassroots anger so evident in November. Still, there are serious fault lines that will not easily be bridged.

Republicans will have only a two-vote margin in the Senate (where Vice President Pence will break a 50-50 tie), and an even smaller margin on key committees. For example, Republicans have just a 9-to-8 majority on the Senate Foreign Relations Committee, meaning a single GOP defection could doom Trump’s nominations or other foreign-policy initiatives.

Even in the House, where Republicans have a much larger — though reduced — majority, House speaker Paul Ryan has seen how even a small, rambunctious minority of Republicans can make his life miserable. With Democrats likely united, every Republican faction will see itself as a potential kingmaker.

President Trump may find “getting things done” harder than he thought. Among the potential flashpoints:

Legislative powers

Donald Trump clearly expects to be a muscular chief executive. Yet, Congress is also waking from its slumber of the Bush–Obama years to reassert its traditional legislative powers. Sen. Mike Lee’s Article I Project is a probable starting point. Lee, and other top Republicans, would reclaim the congressional “power of the purse,” and would limit the ability of executive agencies to act without explicit congressional authorization.

As Lee puts it, “We have taken an oath to defend the Constitution, and the Constitution invests the legislature with the legislative powers.” If President Trump expects to follow President Obama’s footsteps, and govern with “a pen and a phone,” he may run into trouble.

War and peace

Trump’s iconoclastic foreign policy is likely to come under attack from both hawks and doves. Already, John McCain, Lindsey Graham, and Marco Rubio have raised concerns over Trump’s Russia policy generally, and his nomination of Rex Tillerson as secretary of state in particular. Meanwhile, Rand Paul has vowed to block the nomination of John Bolton and similar hardliners to any position at the State Department. We should expect everything from Russia sanctions to the Iran nuclear agreement to the War on Terror to reveal similar splits.

Spending and the debt

Trump has largely abandoned traditional Republican concern over the $20 trillion national debt and resistance to government spending, but many congressional Republicans are likely to feel differently. Speaking for fiscal conservatives in the House, Idaho Republican representative Raul Labrador told reporters, “We are not going to vote for anything that increases the national debt.” Trump’s plan to spend $1 trillion or more on infrastructure is already in trouble. “We know we’re going to have to pay for this,” said Senator John Cornyn, the second ranking Republican in the Senate. “The question is whether we do it now or whether we send it to our kids and grandkids and make them pay for it.” In the House, Speaker Ryan has suggested that infrastructure spending is not high on his agenda. Concern over the debt could even pose problems for Trump’s proposed tax cuts, with Mitch McConnell expressing his desire that any tax-reform measure be revenue-neutral.

Trade

Congress will likely join President Trump’s skepticism of new trade deals, meaning the Trans-Pacific Partnership and similar deals are in real trouble. But congressional Republicans will be far more reluctant to support President Trump’s call for higher tariffs. “I don’t want to get into some kind of trade war,” warns House majority leader Kevin McCarthy.

Immigration

No issue was more central to the Trump campaign than restricting immigration, but even here he may find congressional resistance. Republicans will almost certainly back Trump’s proposals to build a border wall (and Mexico will not be paying for it) and crack down on criminal aliens. But immigration doves, including Lindsey Graham and Arizona senator Jeff Flake, are expected to challenge Trump over the status of the so-called Dreamers under the Delayed Action for Childhood Arrivals (DACA) program.

Replacing Obamacare

Even on an issue like replacing and repealing the Affordable Care Act, there are deep splits in the GOP that may bedevil a Trump administration. Republicans are expected to put a repeal bill on Trump’s desk shortly after he takes office, but because they haven’t yet reached consensus on a replacement, repeal of Obamacare will not likely be immediate. Rather, the legislation will establish a sunset date, say 2018 or 2019, at which point the law will end. But eventually, Republicans will have to make good on a replacement plan. Free-market advocates may rally around a proposal by Flake and Virginia representative David Brat to radically expand health-savings accounts. But Tom Price, who Trump has chosen to head the Department of Health and Human Services, has his own plan that relies heavily on tax credits and retains parts of Obamacare’s subsidies and regulatory structure.

The bottom line should both temper the enthusiasm of Trump enthusiasts and calm the more hysterical fears of Trump opponents.

The Founding Fathers designed a system of government under which legislating is hard to do. That reality has frustrated nearly every president, doing a pretty good job of preventing some of the worst presidential policies.

President Trump is about to run headlong into that reality.

Michael Tanner is a senior fellow at the Cato Institute and the author of “Going for Broke: Deficits, Debt, and the Entitlement Crisis.” Send comments to awoods@tribtown.com