The top House Republican took aim at the nature of American politics in remarks viewed as a rebuke of GOP presidential front-runner Donald Trump and the tone of his campaign.

"This has always been a tough business, and when passions flare, ugliness is sometimes inevitable. But we shouldn't accept ugliness as the norm," House Speaker Paul Ryan said in a speech Wednesday on Capitol Hill.

"Personalities come and go. But principles? Principles endure," Ryan added.

The Wisconsin Republican's address — hastily announced Tuesday before a two-week Easter break — comes as Trump and Sen. Ted Cruz, R-Texas, continue to engage in personal insults on the campaign trail.

The latest flare-up involves a spat over a Cruz-allied superPAC that used a semi-nude photo of Trump's wife, Melania, in an attack ad aimed at alienating the businessman from Utah's Mormon voters. Trump responded on Twitter with a vague threat to "spill the beans" on Cruz's wife, Heidi.

In contrast on Wednesday, Ryan said he has made it his "mission as speaker to raise our gaze and aim for a brighter horizon."

Ryan has pledged to support Trump if he is the nominee, but he has also publicly rebuked the front-runner on several occasions.

Ryan criticized Trump for calling to ban Muslims from entering the U.S., for not more swiftly condemning white supremacists that support his campaign and for not doing more to quell violent outbursts at his campaign events.

"It did not used to be this bad, and it does not have to be this way," Ryan said Wednesday.

Trump at the top of the ticket has shaken up the political battleground for down-ballot races. Republicans are still favored to maintain House control; however, the nonpartisan Cook Political Report recently shifted 10 House races toward Democrats' favor.

Trying to distinguish House Republicans from the politics of the presidential race, Ryan is driving an effort in the House to unveil a policy agenda later this year that will provide a platform for his members to run on in November.

As speaker, Ryan will also chair the GOP convention in Cleveland this July. He has said House Republicans' policy efforts could also provide a platform for the eventual GOP nominee.

But Trump and Ryan fundamentally differ on policies affecting trade, immigration and entitlements like Medicare and Social Security, and it is unclear how the two could reconcile their ideas to run as a unified party in the general election.

The division in the party has led to wild speculation that Ryan, who ran on the 2012 ticket as Mitt Romney's vice president, could somehow exit the convention as the party's nominee if no candidate walks into Cleveland with the nomination locked up.

Ryan has laughed off the chatter as ludicrous.

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