DES MOINES — One of the leading Democratic super PACs, Priorities USA, will spend $50 million more than previously announced against President Trump before the Democratic National Convention, with plans to make nearly $30 million in TV ad reservations in the coming days.

The super PAC, which had announced a $100 million campaign in early 2019, has increased its preconvention budget to $150 million, according to Guy Cecil, the committee’s chairman. “Donors are stepping up earlier than they have before,” he said.

The group will begin booking $30 million in television ads across four battleground states — Florida, Michigan, Pennsylvania and Wisconsin — later this week, as well as $40 million on digital platforms like YouTube, Hulu and Pandora. The first television ads are slated to appear in Wisconsin at the end of February, with ads in the other three states beginning to air in the middle or end of March. The Democratic convention will be held July 13 to 16 in Milwaukee.

“These are the four closest states in any way you want to measure,” Mr. Cecil said.

The television ad campaign will go live months earlier than the group’s first anti-Trump television ads did in 2016, when they began to air in May. Mr. Cecil said more bookings were coming. “I would emphasize ‘so far,’” he said of the reservations.