People were surprised by the news of Moshe Leon's municipal party uniting with Nir Barkat's party, with supposedly some sort of deal in place that Barkat would not run again for mayor in the next elections (3.5 or so years). The expectation is that Barkat plans to leave municipal politics for national politics. This would theoretically leave the field wide open for Moshe Leon to be the next mayor of Jerusalem. It seems he is expected to have the support of [at least some of] the Haredi parties as he did last time, along with Nir Barkat's supporters.

I think Moshe Leon is in for a surprise.

If he thinks he can waltz in and take Nir Barkat's place just because he has some sort of deal to take over the party, he is going to have to work a lot harder than he thinks.

Even if Barkat does leave municipal politics..

First of all, there is no guarantee, at all, that the secular and dati voters will rally around and unite behind Moshe Leon the way the supported Barkat. It took a unified campaign and support for Barkat to win, and there is no reason to assume Leon will have the support Barkat did. I don't see the secular of Jerusalem agreeing so quickly on Leon as the identity of their next mayoral candidate. They will remember that Leon was supported last time by [most of] the Haredi community, and they will be hesitant to give him their support.

Second, the Haredim don't often give losers a second chance. They supported him last time and he disappointed them. He also has not been a strong advocate for them since then. I do not see the haredi community supporting him so quickly or easily in any upcoming elections. They may see an opportunity for their own Haredi candidate to have a good chance of winning, with no unified secular support for Leon and therefore the secular vote likely being split. If the Haredim do not fight too much with each other but unify behind one single candidate, they could have a good chance of defeating a candidate like Moshe Leon.