• President Trump decided on his Supreme Court pick as of Monday afternoon, a source tells CNBC, but the name of the nominee wasn't made public.
  • America First Policies is preparing to unveil a seven-figure ad campaign to back Trump's choice to replace the retiring Justice Anthony Kennedy.
  • Trump plans to announce his nominee at 9 p.m. ET on Monday.
Sen. Heidi Heitkamp, D-N.D., left, listens as President Donald Trump speaks in the Roosevelt Room of the White House in Washington. 

A pro-Trump organization is getting ready to go to war in support of President Donald Trump's Supreme Court nominee, with a plan targeting Democratic senators in red states.

America First Policies is preparing to unveil a seven-figure ad campaign to back Trump's choice, whomever it is, to replace the retiring Justice Anthony Kennedy, according to Erin Montgomery, the group's spokeswoman.

Trump plans to announce his nominee at 9 p.m. ET on Monday. A source familiar with the process told CNBC that Trump had made his decision as of Monday afternoon. However, he had yet to divulge the nominee's name to his team overseeing the process, a separate source said.

The group, she added, plans to target individual states, while paying particularly close attention to the actions of Democratic Sens. Joe Manchin of West Virginia, Joe Donnelly of Indiana, Bill Nelson of Florida, Jon Tester of Montana, Claire McCaskill of Missouri, Heidi Heitkamp of North Dakota and Doug Jones of Alabama. All of them represent states Trump won in 2016.

With the exception of Jones, all of the potential targets are fighting for re-election in the 2018 midterm elections. Jones, who won a shocking December special election victory to flip Jeff Sessions' Alabama seat to blue, is up for re-election in 2020.

For America First, all options are on the table to push Trump's nominee through the Senate, including television, radio, digital and phone ads.

Republican lawmakers could also see their names included in the America First Policies ads.

"We expect all Republicans to be on board at this time," Montgomery said. "Should that change, we will assess but also recognize that we may need to defend those who will be under attack from the radical left."

CNBC reported a week ago that the America First Action super PAC was planning to "encourage" Democratic senators to back Trump's nominee.

CNBC previously reported that the president had suggested to a small group that he had already settled on who he wants to see succeed Kennedy. At the time, he indicated he was in favor of D.C. Circuit Court of Appeals Judge Brett Kavanaugh, but sources insisted he could always change his mind.

Over the July Fourth weekend the president was reportedly lobbied by the likes of Kentucky Republican Sen. Rand Paul and former Pennsylvania Sen. Rick Santorum to pick 3rd Circuit Judge Thomas Hardiman.

NBC News reported Sunday that Trump is focusing mostly on Kavanaugh and Hardiman.

Going into the announcement Monday, sources close to Trump said Kavanaugh is still the front-runner to become the next member of the Supreme Court, but Hardiman's stock has risen in recent days.

The White House did not return requests for comment at the time of publication.

For America First Policies, it is joining the likes of other conservative factions looking to give a boost to Trump's Supreme Court nominee.

The Judicial Crisis Network, a group dedicated to promoting conservative judicial nominees, has said it will launch a $1.4 million ad buy on national cable, digital and in four states: Alabama, Indiana, North Dakota and West Virginia. The ad will feature an introductory bio about Trump's pick and is expected to run for one week.

Americans for Prosperity, a group backed by industrialist Charles Koch is also preparing to unleash a seven-figure campaign in support of the president's nominee.

The group has yet to reveal details of its plan as it is waiting for Trump's announcement because it insists the nominee will have to be from the presidents original judicial list from 2017 and the person will have to have similar traits to Justice Neil Gorsuch.

AFP's extensive work to push for Gorsuch to become part of the Supreme Court last year included its grass-roots organizations launching three waves of direct mail campaigns and a series of targeted digital ads in 12 key states in support of him.