Mr. Romney told Fox News he will skip the Iowa debate, which has been criticized by some Republicans as a distraction.
Mr. Trump, a New York real estate magnate and reality-show star, considered his own run for the 2012 Republican presidential nomination earlier this year.
Panel to subpoena Corzine on MF Global
The trading firm filed for bankruptcy on Oct. 31 after a disastrous bet on European debt. Nearly $1.2 billion is estimated to be missing from customer accounts.
Sen. Debbie Stabenow, chairman of the Senate Agriculture Committee, said Mr. Corzine’s testimony at the Dec. 13 hearing is essential to learn what happened. The vote comes just days after the House Agriculture Committee took similar action to force Mr. Corzine to appear at a hearing Thursday.
Mr. Corzine, a Democrat, represented New Jersey in the Senate from 2001 to 2005. He later served as the state’s governor. The subpoena marks the first time a member of Congress has been forced to testify before his former peers since 1908.
Regulators are investigating whether MF Global used money from customers’ accounts for its own needs as its financial condition worsened. That would violate securities rules. The FBI also is investigating to see if the firm violated any criminal laws.