It’s often said that kinship runs deeper than friendship. Lately, when it comes to chumminess among world leaders and their colleagues in neighboring countries, friendship has trumped citizenship.

Until recently, it was rare to find leaders willing to forge friendships with candidates across borders or to find would-be leaders campaigning inside foreign countries. There are good reasons for that: Candidates who cross these lines can find it harder to win elections or to govern once the electoral test is passed. Their foreign friends can pay a price for backing the wrong horse and for forfeiting a bit of diplomatic leverage once they find themselves sitting across the bargaining table from the man or woman they campaigned against. Consider three current examples.

Angela Merkel and Nicolas Sarkozy

German Chancellor Angela Merkel’s support for the re-election bid of French President Nicolas Sarkozy is especially startling. It’s hardly surprising that Merkel wants Sarkozy to win. The two leaders have forged a durable personal relationship as they navigated their way through Europe’s ongoing crisis of confidence. The French and German leaders deserve considerable praise for their well-coordinated bid to bolster the euro zone.

But for Merkel, there’s a big difference between privately willing Sarkozy on and campaigning at his side across France – particularly at a time when Sarkozy trails Socialist Party challenger François Hollande significantly in opinion polls. Given the populist mood in France, Merkel’s stated reasons for supporting Sarkozy – that he is a conservative candidate whose party is philosophically aligned with her own Christian Democratic Union – sounds less like a boost for his campaign than a nail in his coffin.

And in the end, Merkel will have important work to do with France’s next president, whoever that turns out to be.