In politics, 24 hours is a lifetime. Journalist Yair Lapid's announcement on Sunday that he planned to run for parliament was the talk of the Knesset on Monday - until it was eclipsed by Noam Shalit's announcement that he would run for a slot on Labor's Knesset list.

But even during his brief hours in the limelight, Lapid did not have unmixed joy. While many politicians welcomed his announcement, others, especially among the opposition, feared he would hurt the very center-left bloc he aspires to lead.

"His entry will strengthen and entrench [Prime Minister Benjamin] Netanyahu," said MK Benjamin Ben-Eliezer (Labor ). "He'll mainly take votes from Kadima, and he'll split the center-left bloc."

That prospect elated Likud MKs. "Lapid will hurt Kadima so badly it will be destroyed," predicted one, Ofir Akunis.

Netanyahu himself declined to comment on the issue.

A Channel 10 television poll published on Monday found that a Lapid-led party would win 16 seats, making it the Knesset's second-largest after Likud, with 30 seats. The main loser would be Kadima, which would plunge to 14 seats, from 28 today. But the balance between the blocs wouldn't budge, the poll found - religious and rightist parties would still have a 63-seat majority.

Moreover, the poll was taken while interest in Lapid was at its peak. There's no guarantee he will maintain that level of support.

But it seems Lapid is already having an effect on Kadima. After months of refusing Kadima members' demands that she advance the party's leadership primary, Kadima chairwoman Tzipi Livni told Channel 2 television last night that she would do so. She added that she welcomed Lapid's entry, but it was "premature to eulogize Kadima."

Lapid himself kept quiet on Monday. Political observers attributed this to his desire to focus all his energies for now on recruiting candidates for his new party - especially since it's not clear when the next election will actually take place.

Nevertheless, a Likud source warned, this silence could backfire. From now on, "everyone will be asking where Lapid is and what he says about things, and if he won't say, they'll claim he's not a leader."

Meanwhile, the government sought to dampen speculation that new elections would be called soon. "I have personal information that the prime minister's intention to advance the Likud primaries is strictly an internal [party] matter," Environmental Protection Minister Gilad Erdan told the plenum. That decision had helped fuel speculation that the general election would also be advanced from next year to this.

Foreign Minister Avigdor Lieberman also joined the effort. Asked how Lapid's entry would change the political map, he responded, "Wait until the elections in 2013."