Trump campaign actively preparing for Harris nomination, sources say

With President Joe Biden dropping out of the presidential race and endorsing Kamala Harris Sunday, ABC News has learned more about how the Trump campaign is preparing should Harris become the Democratic nominee for president.

The Trump campaign is preparing new ads to attack Harris' record, and is compiling opposition research books and conducting polling to test her weaknesses in a general election matchup, sources familiar with the plans told ABC News.

The campaign has also started digging through the records of potential running mates for Harris, including Pennsylvania Gov. Josh Shapiro.

The attack ads being prepared focus on Harris' role leading the Biden administration's effort on the migrant crisis, accusing the administration of failing to secure the border with Harris in charge, according to sources.

In addition to ads, the Trump campaign is also preparing to mash up clips of Harris' statements, particularly her laughing during events and interviews, sources said.

While the Trump campaign is focused mostly on Harris, it's also prepared opposition books on several other Democrats with presidential ambitions, sources said.

Trump's advisers had privately hoped President Biden would stay in the race, believing the questions about his mental fitness and age, and his low approval ratings, would have helped Trump in November, according to sources.

After Biden's halting debate performance last month, the Trump campaign held back advertising that could further damage Biden, one source said.

The New York Times was the first to report these developments.