He said he believes Santorum is losing momentum after losses this week in Arizona and Michigan, as well as Wyoming’s caucuses.

Romney has tallied more delegates so far in the GOP race, but Santorum has continued to challenge him in the polls. Newt Gingrich and Ron Paul are also still contenders, but Gingrich has only won one state and Paul has not taken the vote in a single state.

Grassley, who has not endorsed a candidate, emphasized that he will support whoever becomes the Republican nominee.

"It'd be intellectually dishonest for me to say it's Romney over somebody else, because if I didn't have guts enough to back Romney when he was a candidate in Iowa, why would I say now for other states that aren't completed that I'd back Romney?" he said.

And he couched his prediction in favor of a quick lock for Romney’s nomination by noting that the race has been unpredictable.

“You've seen every candidate leading everybody in some of it, even including [President] Obama, and they're up one month and down the next month, so how do you know for sure?" he said.