'This Week' Transcript: Secretary of State John Kerry

— -- Below is the rush transcript for "This Week" on April 12, 2015. It may contain errors and will be updated.

ANNOUNCER: On ABC This Week, breaking right now just minutes away from Hillary's big announcement, the biggest frontrunner in history, the Clinton machine hitting high gear.

Plus, Rand Paul is now in, Marco Rubio is next. So, which Republican has the best shot against Hillary? Complete insights and analysis on all the breaking 2016 news from our powerhouse political team.

And from Mike Huckabee, the GOP contender who knows Hillary best.

And deadly shooting, the new video and mystery eyewitness in that stunning case of a South Carolina officer charged with murder. How does a routine traffic stop turn deadly.

From ABC News, This Week with George Stephanopoulos begins now.

GEORGE STEPHANOPOULOS, HOST: Good morning. A generation away from her family's first White House bid, Hillary Clinton kicks off her second run for president today.

It will look and feel a little different from last time out, but has she learned the right lessons? Can Democrats hold the White House for a third term? How will the GOP take her on?

Our team here to analyze all those questions this morning and our Clinton correspondent Cecilia Vega starts us off from Brooklyn where Team Hillary is based. Good morning, Cecilia.

CECILIA VEGA, ABC NEWS CORRESPONDENT: George, good morning to you. A beautiful morning out here in Brooklyn. And that campaign is already in full swing mood.

But let me tell you about what this announcement is going to look like today, now just a few hours away.

You know, these big political rallies that we've seen from candidates in the past? You're not going to see the balloons, you're not going to see the signs of supporters from Hillary Clinton today, what you're going to see is an announcement on social media, probably on Twitter. We also know that there will be a video, which she has already filmed.

After that announcement today, Hillary Clinton will then head to Iowa where we understand she's going to be meeting with voters, but they're going to be small meetings, what's being called one on one sessions, these kind of private discussions.

Her supporters are ready for this fight, they are already out there rallying. We saw a rally here in New York City yesterday called the Ready for Hillary rally. And they are ready to kick off this race.

George, this is a really well-oiled machine. And they say they are intent on not repeating the mistakes of the past.

STEPHANOPOULOS: Hey, one of those mistakes in past campaigns, Team Hillary has been kind of wracked by infighting. Her new campaign manager Robby Mook, young campaign manager, is laying down the law on that.

VEGA: Yeah, that's right, he sent this memo out to staffers yesterday. And we got ahold of it. And essentially this outlined some of the general principles of this campaign. And the implication really is that there will be -- they will try to have less infighting. I want a quote from a couple of his lines of this memo, because like I said we got ahold of it.

So, Mook tells the staffers, "when we disagree, it's never personal. Once a decision is made, we execute it together." He says, "this campaign is going to be about strategy and not one-offs," George. So I think it's pretty clear here we go, 2016.

STEPHANOPOULOS: Let's see if they can hold to that.

OK, Cecilia, thanks very much.