Republicans should not get ahead of themselves and assume they will make large gains on the Democrats' majorities in Congress, Sen. John McCainJohn Sidney McCainCummings to lie in state at the Capitol Elizabeth Warren should concern Donald Trump 'bigly' Lawmakers toast Greta Van Susteren's new show MORE (R-Ariz.) cautioned Thursday night.

In a Fox News interview with Greta Van Susteren, McCain spoke about the tough economic climate and the angry electorate it has bred, suggesting the GOP needs to follow through with a strong campaign message to win big in the November midterm elections.


"And I want to emphasize one other thing: Don't take anything for granted. We will celebrate after the election results are in," he said. "Please, let's not anticipate a great victory, and let's give the American people a positive agenda that they can support."

McCain last week became one of the highest-profile Republican lawmakers to say that his party could take control of the Senate through the elections. But on Thursday, the 2008 GOP presidential nominee cautioned that the accomplishment will not come easily.

The party would need to perform extraordinarily well on Nov. 2 to win a majority. Democrats currently have 59 seats in the Senate, meaning that Republicans would need to win virtually every competitive race this year in order to take the 10 seats necessary to take control.

Election handicappers had as recently as last week projected that the Senate is in play for Republicans, but many adjusted their expectations after a stunning Senate primary victory in Delaware by Tea Party-backed candidate Christine O'Donnell over centrist GOP Rep. Mike Castle.

Political observers and some GOP strategists have said that past controversial statements made by O'Donnell and her conservative views won't allow her to win the general election against Democrat Chris CoonsChristopher (Chris) Andrew CoonsMeet the dog and 'sea turtle' who launched campaigns for office Senators demand briefing on Trump's decision to withdraw from Syria 2020 Democrats push for gun control action at forum MORE in blue Delaware, putting Republican hopes of winning the Senate in doubt.

McCain said that O'Donnell could win, but that it would be an uphill climb.

"I think she will do nothing but go up between now and the election," he said. "Whether she can win the election or not, I'm not sure about that. And I don't think there's any doubt that if she can pull off a surprise in the primary as she did, then I'd watch out for her in the general."

McCain, who unlike Castle was able to fend off a primary challenge from the right, added that "anybody who thinks that incumbency and past service will qualify them for reelection" is "making a serious mistake."