'This Week' Transcript: White House Chief of Staff Denis McDonough

September 14, 2014 — -- Below is the rush transcript of "This Week" on September 14th, 2014. It may contain errors.

ANNOUNCER: ABC's This Week. Breaking News, ISIS releases another chilling execution video. This time, a British hostage. How will the UK respond.

Plus, President Obama making his case to destroy the jihadist army. What does it mean for our troops, our safety? Are we really at war? This morning, answers.

Plus, breaking developments from our global team: Footbal furor. That shocking video provoking a conversation about the hidden epidemic. Domestic violent across America.

And Hawkeye bound -- Hillary's first trip to Iowa in six years. Jon Karl and our powerhouse roundtable are on the road in Iowa.

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

MARTHA RADDATZ, HOST: Good morning, I'm Martha Raddatz.

We begin with breaking news, another horrifying execution video released by ISIS. The victim, a husband and father, British aid worker David Haines.

British Prime Minister David Cameron speaking just over an hour ago, calling Haines a hero and warning that the UK must confront what he calls the ISIS menace.

We're covering all angles of the story this morning. And let's start off in the region with ABC's Alex Marquardt.

Good morning, Alex.

(BEGIN VIDEOTAPE)

ALEX MARQUARDT, ABC NEWS CORRESPONDENT: Good morning, Martha.

The brutal murder of British aid worker David Haines has been called by Britain's prime minister an act of pure evil. ISIS says its retribution for Britain joining the American led coalition against the militant groups, a growing alliance that the U.S. has working on intensely for most of the past week to confront the ISIS threat.

(BEGIN VIDEOTAPE)

MARQUARDT: David Haines had only been in Syria for a few days helping deliver aid to a refugee camp when he was kidnapped early last year. This weekend ISIS released a grizzly video of the 44-year-old's beheading, a warning, they said to the allies of America.

This latest chilling tape comes as the American military assault against ISIS grows, so far 160 airstrikes against targets in Iraq, a campaign the U.S. now wants to expand with the support of not just western allies, but regional friends as well, like Saudi Arabia where Secretary of State John Kerry told me that he and the president want the largest coalition possible.

JOHN KERRY, U.S. SECRETARY OF STATE: Because the bigger it is the more effective it is, the faster we can eliminate the threat.

MARQUARDT: While some have eagerly signed up, others have been more reluctant. Egypt said on Saturday, it supports the mission, but didn't say whether it would contribute.

Turkey has been the biggest gateway for foreign fighters into Syria, but wants to stay behind the scenes.

And as ISIS faces an international assault, its ranks are growing. A new CIA estimate says ISIS now has between 20,000 and 32,000 fighters.

(END VIDEOTAPE)

MARQUARDT: That number is only growing by the day. And so far despite those U.S. airstrikes, ISIS has managed to hold on to most of the territory it has taken in Iraq and Syria. Even once this international coalition is finalized, the Obama's administration admits it will take years to defeat ISIS, a war that will almost certainly be handed off to the next administration -- Martha.

RADDATZ: Thanks, Alex.

More now on this horrific new video and the fallout. ABC's chief investigative correspondent Brian Ross is in New York. And ABC's Hamish McDonald is in London tracking all the reaction there.