Romney was the leader in recent polls in early primary or caucus states of Iowa and New Hampshire, and he has raised $21 million in the first quarter of 2007, the Chicago Tribune reported.
The Tribune said that Romney also handled himself well in the first two Republican debates.
Opponents like to point to Romney's changing positions on issues such as abortion, which he opposes, and gun rights, which he support.
"Mitt Romney has been consistent in one regard: that nearly every position he holds now is opposite of what it was when he was governor of Massachusetts," Brian Jones, spokesman for the campaign of U.S. Sen. John McCain, R-Ariz., told the Tribune.
Romney said that change comes with experience.
"You don't change your principles but your view on a particular issue may change," he said to the newspaper.