PARIS — To win re-election in the runoff on May 6 against the Socialist François Hollande, Nicolas Sarkozy will need the support of right-wing voters who have turned their backs on him, disappointed with his presidency.

But there are serious questions as to whether he can win them over, and even if he does, a strong shift to the right would make his European partners uneasy. The next two weeks of the campaign are likely to put a united Europe even more in the cross hairs, with Mr. Sarkozy calling for more protectionism and Mr. Hollande for more growth and easier money, challenging the German calls for austerity.

Already on Monday, major European leaders from Germany’s chancellor, Angela Merkel, to Sweden’s foreign minister, Carl Bildt, said they were disturbed by the level of support for the far right in France, and the markets are worried that the elections may disrupt efforts to solve the region’s debt and banking crisis.

Mr. Sarkozy won the presidency five years ago by attracting many supporters of the far-right National Front, but in Sunday’s first round, they deserted him, voting instead for the party’s own candidate, Marine Le Pen, who won about 18 percent of the ballots cast, a record for her party. Mr. Sarkozy won 1.6 million votes fewer than he did in the first round of 2007, when he got about 31 percent of the vote, compared with about 27 percent on Sunday.