McConnell, interviewed on CNN's "State of the Union," stopped short of a formal endorsement of Romney while saying that "the chances are overwhelming" that he will be nominated and that he would be "an excellent candidate."
"It's time to turn our attention to the fall campaign and begin to make the case against the president of the United States," the Kentucky Republican said, echoing comments made by Ryan on both ABC and CNN Sunday.
Romney has predicted victory in the Wisconsin primary, projecting new confidence that such a win would clear the way for him to lock up his party's presidential nomination.
"We're looking like we're going to win this thing on Tuesday," he said Saturday in Fitchburg, Wis., suggesting he could also come out ahead in the other April 3 contests as well. "If I can get that boost also from Wisconsin, I think we'll be on a path that'll get me the nomination well before the convention."
Romney's chief rival for the nomination, former Pennsylvania Senator Rick Santorum, said Sunday on "Fox News Sunday" that he felt no pressure to drop out of the race.
Romney "isn't even close to closing the deal" and Democrats showed in 2008 that a long primary can produce the best candidate, said Santorum, who according to the AP tally has 273 delegates.
"We came up with someone who, well, just simply wasn't able to win" in 2008, Santorum said. "We don't need to bail out and not have the best candidate to take Barack Obama on in the fall."
Santorum said that primary elections to be held in April and May in Texas, Indiana, Pennsylvania and North Carolina "look very, very good" for him.
The Wisconsin primary is Santorum's last opportunity to demonstrate his strength in the Midwest, a region where he has said he would be better than Romney in competing against Obama. Santorum held Romney to wins of three percentage points in Michigan and one percentage point in Ohio.
The Wisconsin primary is not "do or die," Santorum said Sunday on NBC's "Meet the Press."
In a NBC News/Marist poll released late last week, Romney led Santorum in Wisconsin, 40 percent to 33 percent. Paul was third with 11 percent, and Gingrich was last at 8 percent. The telephone poll of 740 likely voters in the state's Republican primary was conducted March 26-27 and has a margin of error of plus or minus 3.6 percentage points.
The next contests will be on April 24 in Rhode Island, Connecticut, New York and Delaware states expected to favor Romney and in Pennsylvania, which Santorum represented in the House and the Senate.
"We have to win Pennsylvania and we're going to win Pennsylvania," Santorum said on NBC Sunday. "I have no doubt about that."
Newt Gingrich, who is third in the race with 135 delegates and hasn't won a primary outside of South Carolina and his home state of Georgia, said on CBS's "Face the Nation" that he would endorse either Romney or Santorum if he doesn't win the nomination because "there's no alternative."
"You didn't say, 'In an ideal world, is Mitt Romney the person I'd like to have as president?' " Gingrich said on CBS. "That person is Newt Gingrich."
Gingrich supporter Sheldon Adelson, chairman of Las Vegas Sands Corp., said last week that the former House speaker is "at the end of his line," according to the Los Angeles Times, which reported that Adelson, his wife and other family members had given a total of $16.5 million to Winning Our Future, a super- PAC supporting the Georgia Republican.
Representative Ron Paul of Texas, who trails the other candidates with 50 delegates, said on CBS that he's "still campaigning" and that he wouldn't expect to be considered as Romney's running mate.
"There's too many disagreements," he said. "I have no common ground on economics."
Paul wants to eliminate the Federal Reserve, which he blames for the nation's "boom-bust" economic cycles, according to his campaign website, and legalize what he calls "sound money" as an alternative to "inflated" U.S. currency.
Reporter Lisa Lerer contributed to this report.