'Start Here': Trump denies pressuring Ukraine; US soldier's alleged plot to bomb news network

It's Tuesday, Sept. 24, 2019. Let's start here.

1. Considering the complaint

President Donald Trump has denied he put pressure on Ukraine to investigate former Vice President Joe Biden in a phone call at the center of a whistleblower complaint, but noted it would "possibly have been okay if I did."

When asked by reporters on Monday about what he discussed with the president of Ukraine during their July 25th conversation, Trump appeared to suggest a link between withholding $250 million in aid for Ukraine and corruption allegations: "If you don't talk about corruption, why would you give money to a country that you think is corrupt?"

The White House is considering whether to release the transcript of the call, sources familiar with the matter tell ABC News Chief White House Correspondent Jonathan Karl. House Speaker Nancy Pelosi has given the Trump administration a Thursday deadline to hand over information related to the complaint as Democrats face renewed pressure to impeach Trump.

2. US soldier arrest

A U.S. soldier who allegedly plotted to attack a major news network and named Beto O'Rourke and a leftist group as potential targets has been arrested on terror charges, according to federal authorities.

Jarrett William Smith, 24, was charged with distributing information about explosives and weapons of mass destruction after he allegedly talked to an FBI informant in an online chat group about placing a "vehicle full of various explosive materials" at the network. Smith, who transferred to Fort Riley, Kansas in July, is also accused of planning to travel to Ukraine to fight with a violent far-right group, officials said.

"I think what these charges show is where the threat is moving," ABC News' Mike Levine tells "Start Here" today. "We're seeing that in the domestic terrorism realm where... far-right Americans are going or talking about trying to join groups in places like Ukraine so that they can then bring those skills back to the U.S. to further their extremist far right views."

O'Rourke's campaign said in a statement, "We’re grateful to the FBI for their diligence in handling this case and for their work to keep our country safe in the face of domestic terror threats."

3. Climate call to action

"You have stolen my dreams and my childhood with your empty words."

Greta Thunberg, a 16-year-old Swedish climate activist, delivered an emotional call to action to world leaders at the United Nations, demanding they act on greenhouse gas emissions.

"You could hear a pin drop when Greta took the stage," says ABC "Nightline" co-anchor Juju Chang. "She basically shamed everyone in the room."

The president, who is set to address the UN General Assembly today, also made a brief surprise appearance at the climate summit, later telling reporters, "I’m a big believer in clean air and clean water, and all countries should get together and do that."

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Elsewhere:

'It is important to remain calm': Already bracing for a tropical system in the next 24 hours, Puerto Rico was hit by a 6.0 magnitude earthquake late Monday.

'It’s still shocking to us': A Florida school resource officer who arrested two 6-year-old students has been fired.

'By the sake of God': Cellphone video captured a harrowing rescue on Monday, showing bystanders who scrambled to rescue a young girl when her father jumped in front of a moving train while holding her in his arms.

'He touched a lot of people's lives': Former college basketball star Andre Emmett was shot and killed outside his home in Dallas in the early morning hours of Monday.

From our friends at FiveThirtyEight:

'It’s obviously great news for Warren': According to a new survey, Elizabeth Warren has 22 percent support among Democrats in Iowa, the crucial first-in-the-nation caucus state. Former Vice President Joe Biden sits at 20 percent, followed by Sen. Bernie Sanders at 11 percent, South Bend, Indiana, Mayor Pete Buttigieg at 9 percent and Sen. Kamala Harris at 6 percent.

Doff your cap:

Legendary actress Demi Moore opened up her home in the Hollywood Hills to ABC News' Diane Sawyer to discuss her past, a devastating crossroads and how she got to where she is today.

Moore defined Hollywood in the '90s in some of the decade's biggest hits, but her fame has not come without loss and isolation. The actress went through a period of anguish nearly seven years ago when she was not speaking to her ex-husband, her three children stopped speaking to her, urging her to get help.

Moore, 56, said, "I lost me."

"I think the thing, if I were to look back, I would say I blinded myself and I lost -- I lost myself," she explained.

She set out to reclaim her life, writing a memoir, "Inside Out," that takes a candid look at her relationships, struggles from her childhood, ascent to fame amid life's pitfalls and her aims to help others who may be struggling. The actress dedicated the book to her three daughters, now very much back in her life, and her troubled mother.

Watch more of Diane Sawyer's interview with Demi Moore this morning on "Good Morning America" on ABC.