Mr. Griffin also gave $5 million to the main Republican Senate super PAC, making him its largest donor in the second half of the year.
In addition, Mr. Griffin gave $5 million to a Pennsylvania-focused super PAC, which has opposed Dr. Mehmet Oz, the surgeon and former television show host running in the Republican primary there. Among his opponents is David McCormick, who is the former chief executive of a prominent hedge fund and who entered the race after the filing deadline.
Dr. Oz contributed more than $5 million to his own race — one of multiple wealthy Republican candidates powering their Senate campaigns with their own money. Jeff Bartos, another Republican candidate in Pennsylvania, gave his campaign $1.3 million.
In Arizona, Jim Lamon, a former energy executive, has put more than $8 million of his own money into his primary Senate run.
In Ohio, the Senate race is crowded with wealthy Republican self-funders who have lent or donated money to their own campaigns: Mike Gibbons, an investment banker ($11.4 million); Jane Timken, a former party chair ($3.5 million); Bernie Moreno, a former car dealer ($3.75 million); and Matt Dolan, whose family owns the Cleveland Guardians ($10.5 million).
Some of Mr. Dolan’s family members put an additional $3 million into a super PAC.
In Alabama, Mike Durant, who was in one of the Black Hawk helicopters that was shot down in Somalia in 1993, put more than $4 million into his run. Mr. Durant faces a former top aide to Senator Richard Shelby of Alabama, Katie Britt, who raised $1.2 million last quarter and has $4.1 million cash on hand.
Mr. Trump has endorsed a third Alabama candidate, Representative Mo Brooks, whose fund-raising has flagged. Mr. Brooks raised only $386,000 in the fourth quarter, down sharply from his previous two quarters.