Senate Majority Leader Mitch McConnell, accompanied by members of his party, speaks at a news conference Wednesday at the Capitol. (Aaron P. Bernstein/Reuters)

The Senate's top Republican on Thursday quashed calls from House leaders to tackle Medicare and Medicaid spending next year, declaring it politically unfeasible and thus off the 2018 agenda.

"I think Democrats are not going to be interested in entitlement reform, so I would not expect to see that on the agenda," Senate Majority Leader Mitch McConnell (R-Ky.) said at a breakfast sponsored by Axios. "What the Democrats are willing to do is important, because in the Senate, with rare exceptions like the tax bill, we have to have Democratic involvement."

McConnell's comments are a direct blow to the agenda of House Speaker Paul D. Ryan (R-Wis.), who has been saying for weeks that Congress will work on ways to reduce spending on Medicare, Medicaid and welfare in the new year.

His statement is also a sign that Senate Republican leaders want to limit the situations in which they are willing to rely on procedural moves to get around Democratic opposition in a high-stakes election year.

Any challenge to entitlement spending could also find opposition in the White House. President Trump, as a candidate, promised he would not cut spending on Social Security, Medicare or Medicaid. In an interview with conservative radio host Ross Kaminsky earlier this month, Ryan said he was working to convince Trump about cutting spending on the programs.

McConnell's dismissal of entitlement changes comes just one day after Republicans cheered themselves for passing the most sweeping tax bill to emerge from Congress in decades, the GOP's first major legislative victory since assuming control of both Congress and the White House.

Republicans passed the tax bill without a single Democratic vote by using the budget reconciliation procedure, which allows certain fiscal measures to pass the Senate without clearing the usual 60-vote hurdle.

The Senate could try to use the budget reconciliation maneuver to reduce federal spending on the entitlement programs. But such reductions are a much more politically treacherous endeavor than the tax overhaul, particularly with the GOP trying to protect a slim 51-vote majority in the Senate next year.

And Democrats are already warning Republicans against attempting to force any reductions to entitlement spending, making it almost certain that if the GOP goes ahead with such changes, they will be doing so without any Democratic support — and exposing themselves to attacks on the campaign trail.

While McConnell said Thursday that he was confident the GOP would keep the Senate majority after the 2018 elections because fewer Republican seats are in play, he warned that "the map alone doesn't guarantee the outcome."