By Emmanuel Jarry
VALENCIENNES, France (Reuters) - Nicolas Sarkozy was joined on the campaign trail on Friday by a prominent, popular centrist politician who gave him a ringing endorsement that should boost the conservative president's popularity among France's crucial middle-of-the-road voters.
Jean-Louis Borloo, a former environment minister, said he was fully behind Sarkozy's re-election bid, lending a potential lifeline for the president's chances in a May 6 runoff which polls say he is set to lose to Socialist Francois Hollande.
The affable, craggy-faced Borlo welcomed Sarkozy to his home turf, in the northern city of Valenciennes, where Borloo was once a popular, hands-on mayor.
Their meeting under sunny skies marked a contrast with the somber mood of recent days when candidates suspended campaigning following a spate of shootings in the southern city of Toulouse. The gunman was killed by police on Thursday.
"It's a beautiful day because it's the first time in five or six days that we've been a bit more relaxed," Sarkozy told reporters.
The election is a two-horse race between Sarkozy and Hollande, who is more popular than the incumbent but has no ministerial or international experience.
Borloo's pledge of wholehearted support should give Sarkozy a further lift after his careful handling of the shooting crisis helped nudge him ahead in some opinion polls for the April 22 first round vote.
Sarkozy has also already narrowed the gap behind Hollande in polls for the May runoff but centrist voters would play a key role in helping Sarkozy to victory.
The centrist vote has been divided among a series of players, of whom Francois Bayrou is the strongest candidate, currently expected to place fourth in the first round.
So courting the supporters of Bayrou and adherents of Borloo in the month before the April election while trying to reassure them that conservatives and centrists share a common vision may pay off for Sarkozy in the runoff.
Borloo quit the government in late 2010 after being passed over for the post of prime minister and his centrist Radical Party broke long-standing ties with Sarkozy's UMP party in May 2011. Borloo toyed with running for president himself, ultimately decided not to, and waited until late in the election race to come out behind Sarkozy.
The two men have had cordial but tense relations since Borloo left Sarkozy's cabinet. Sarkozy said on Friday that the pair were "still friends."
In an interview in daily Le Figaro, Borloo said he was in favor of recent pledges by Sarkozy to impose a minimum tax on large, listed companies, crack down on wealthy tax exiles and provide professional training for welfare recipients.
"These measures correspond to our program," Borloo said. "I am committing myself at his side for a fair France and to add my weight to the campaign before the first round. I will use all my energy and power."
The Radical Party's priorities include giving a second chance to over-indebted families, supporting children struggling in school, improving access to housing for employed workers and creating 150,000 apprenticeships for problem youth.
(Writing by Alexandria Sage; Editing by John Stonestreet and Robin Pomeroy)