'This Week' Transcript: Sen. Bernie Sanders, Reince Priebus, and Charles Koch

— -- THIS IS A RUSH TRANSCRIPT FOR 'THIS WEEK' ON April 24, 2016 and it will be updated.

ANNOUNCER: Starting right now on THIS WEEK with George Stephanopoulos, is this the real Donald?

DONALD TRUMP (R), PRESIDENTIAL CANDIDATE: I sort of don't like toning it down, you know?

ANNOUNCER: The new signs that Trump is trying to make a presidential pivot.

But can the brash frontrunner tone it down enough to finally get the GOP behind him?

We're asking the Republican Party chair about the Trump transformation.

Plus, one of the ultra secretive billionaire Koch brothers breaks his silence about the 2016 race in a revealing ABC News exclusively.

JONATHAN KARL, ABC NEWS CORRESPONDENT: So is it possible another Clinton could be better than another Republican this time around?

CHARLES KOCH, KOCH INDUSTRIES: It's possible.

It's possible.

ANNOUNCER: And Bernie's long shot campaign.

SEN. BERNIE SANDERS (I-VT), DEMOCRATIC PRESIDENTIAL CANDIDATE: I am in this race to the end.

ANNOUNCER: He's pushing harder than ever despite a nearly impossible path to the nomination. With tough contests ahead, will he damage Hillary Clinton before he's done?

Bernie Sanders speaks out live.

From ABC News, it's THIS WEEK.

Here now, chief anchor, George Stephanopoulos.

GEORGE STEPHANOPOULOS, ABC HOST: Good morning.

Donald Trump is riding high after his crushing win this week in New York, poised to pull away with a possible sweep in Tuesday's primaries. And now his team is reaching out to the GOP with the promise of a more presidential Trump,

But can the candidate pull it off?

Does he even want to?

And will that be enough to win over the Republican Party?

GOP Chair Reince Priebus and our roundtable standing by to weigh in.

ABC's Tom Llamas starts us off.

(BEGIN VIDEOTAPE)

TOM LLAMAS, ABC NEWS CORRESPONDENT (voice-over): For all of that talk, Donald Trump would tone it down...

TRUMP: I sort of don't like toning it down...

LLAMAS: -- the candidate has turned it up.

On Ted Cruz, just last week, he called him "Senator." Now this.

TRUMP: He's got zero personality because he lies like a thief, OK?

LLAMAS: A step back. Remember, this was to be the week Donald Trump would make a presidential pivot, working off the presidential checklist. An op-ed in "The Wall Street Journal," a big foreign policy speech Wednesday at the National Press Club that he'll deliver with the help of a teleprompter.

Going up with warmer ads.

(BEGIN VIDEO CLIP FROM CAMPAIGN AD)

UNIDENTIFIED MALE: My father will make an incredible president.

(END VIDEO CLIP)

LLAMAS: All to show the Republican Party he's ready to step up.

Then this, in Florida, at the RNC spring conference, Trump's top adviser, Paul Manafort, caught on tape telling a private meeting of top Republicans that underneath the rough and tumble primary persona, there's a more polished, more presidential reality.

PAUL MANAFORT, CAMPAIGN MANAGER, DONALD TRUMP: He gets it. The part he's been playing is (INAUDIBLE) is a part that now you've been expecting.

LLAMAS: And just like that, the primary now a fight over the truth about Trump,

SEN. TED CRUZ (R-TX), PRESIDENTIAL CANDIDATE: Donald Trump is a master illusionist. He is the Harry Houdini, engaged in an act of misdirection. Trump is a phony.

LLAMAS: Trump fired back, attacking Cruz.

TRUMP: He walks in bible held high. Then he puts the bible down and then he lies. He's a liar.

LLAMAS: Telling another crowd, if he wasn't who he was, he wouldn't be ahead and they wouldn't be there.