Emerging from two years of relative silence, former House Speaker Paul Ryan has joined the fight against Donald Trump, urging fellow conservatives to reject the former president's divisive politics and those Republican leaders who emulate him.

Ryan made his remarks during a Thursday evening address at the Ronald Reagan Presidential Library in California. He was critical of both Republicans and Democrats, though he saved his sharpest barbs for Trump, who is by most measures the leader of the modern-day Republican Party.

“It was horrifying to see a presidency come to such a dishonorable and disgraceful end,” Ryan said, referring to the deadly attack on the U.S. Capitol that Trump inspired on Jan. 6.

“Once again, we conservatives find ourselves at a crossroads,” Ryan continued. “And here’s the reality that we have to face: If the conservative cause depends on the populist appeal of one personality, or on second-rate imitations, then we’re not going anywhere. Voters looking for Republican leaders want to see independence and mettle. They will not be impressed by the sight of yes-men and flatterers flocking to Mar-a-Lago.”

Trump fired back on Friday, describing Ryan as “a curse to the Republican Party.”

It's unclear how much impact Ryan's words will have in the broader fight for the future of the GOP, if any. Ryan, the 2012 Republican vice presidential nominee, was among the most respected Republicans in the nation’s capital before Trump’s rise, but two years out of office, his open contempt for Trump is not in line with the vast majority of Republican voters and elected officials.

A tiny but growing group of anti-Trump Republicans has struggled to steer the party in a new direction, even as Trump continues to promote the same false claims — that he would have won the 2020 election if not for mass voter fraud — that inspired the Capitol insurrection. At the same time, Trump is openly contemplating another presidential run in 2024.

In a statement released the morning after Ryan's speech, Trump blamed the Wisconsin Republican for the GOP's loss in the 2012 presidential contest, when Ryan served as Mitt Romney's running mate.

“He has no clue as to what needs to be done for our Country, was a weak and ineffective leader, and spends all of his time fighting Republicans as opposed to Democrats who are destroying our Country,” Trump said in a written statement. “As a Republican, having Paul Ryan on your side almost guarantees a loss, for both you, the Party, and America itself!”

Ryan spoke Thursday as the opening speaker for the Reagan library’s “Time for Choosing” series, which will later feature 2024 Republican presidential prospects such as former Vice President Mike Pence, former U.N. Ambassador Nikki Haley and former Secretary of State Mike Pompeo.

Those close to Ryan, 51, do not expect him to run for public office again, but they suggest he is paying close attention and remains concerned about the future of the party. Ryan also sits on the board of Fox Corp., which owns Fox News.

In his remarks, Ryan described President Joe Biden's agenda as “more leftist than any president in my lifetime" and warned of exploding federal spending under the Democrats who control Washington. He lamented the GOP's interest in culture wars and “identity politics” at the expense of conservative principles.

“Culture matters, absolutely yes, but our party must be defined by more than a tussle over the latest grievance or perceived slight," he said. "We must not let them take priority over solutions — grounded in principle — to improve people’s lives.”

The Republican Party has an opportunity to win elections and address critical policy challenges, as long as they don't get in their own way, Ryan continued.

“If we fail this test, it will be because the progressive left will have won by default,” he said. “It will be because the conservative cause ... lost its way and followed the left into the trap of identity politics, defining itself by resentments instead of by ideals. It will be because we mistake reactionary skirmishes in the culture wars with a coherent agenda. It will be because we gave too much allegiance to one passing political figure and weren’t loyal enough to our principles."