CAIRO â€"  Egypt's wide-open presidential election, which was in its second day of voting Thursday, is showing how deeply polarized the nation has become, with backers of rival Islamists and former regime figures each vowing they cannot let the other rule.

The impact of their rivalry goes beyond the key question of who gets to rule Egypt for the next four years.

An Islamist president will mean a more religious government, while a figure from Hosni Mubarak's ousted regime occupying the land's highest office would likely keep Egypt locked in dictatorship and thwart democracy.

The two candidates that inspire the most polarized opinions are Mohammed Morsi of the Muslim Brotherhood, the country's largest political group, and Ahmed Shafiq, a former air force commander and Mubarak's last prime minister, who was booted out of office by street protests several weeks after his former boss.

In the Mediterranean port city of Alexandria, the mother of a young businessman who was beaten to death by policemen in 2010 warned of a "second revolution" if one of the "feloul" - a member of the Mubarak regime, like Shafiq - is elected. The killing of her son, Khaled Said, helped ignite the uprising against Mubarak last year.

"I don't feel that my son has received justice," Said's mother, Laila Marzouk, said Thursday after she voted for Hamdeen Sabahi, a leftist candidate who is a favorite among revolutionaries. "If one of the feloul of Mubarak's regime wins, another revolution will start and I'll be among the first to take part."

Beside Shafiq, the only other Mubarak regime figure running is Amr Moussa, who served as foreign minister for 10 years before he became the Arab League chief in 2001.

Both Shafiq and Morsi have repeatedly spoken of the dangers, real or imaginary, of the other becoming president. Morsi has said there would be massive street protests if a "feloul" wins the vote. They can only win if an election is rigged, he warned.

Shafiq, on his part, has said it would be "unacceptable" if an Islamist takes the presidential office, echoing the rhetoric of Mubarak, his longtime mentor who devoted much of his 29-year rule to fighting Islamists. Still, Shafiq's campaign has said it would accept the election's result.

While a Shafiq victory could spark protests, the deeper problem is whether Egypt's multiple power centers will be able to work together no matter who wins. Egyptians are eager for the new leader to rebuild the nation, wracked by more than a year of unrest, crime and a faltering economy.

A major issue is how a president will get along with the Islamist-dominated parliament, where the Brotherhood alone holds nearly half the seats and ultraconservatives known as Salafist have another 20 percent.

Also looming is the writing of a new constitution, already the source of contention. The Brotherhood and Islamists tried to control the panel tasked with writing the charter, sparking a backlash that led to the dissolving of the panel by a court ruling.

There is also the question of the powers that should be retained by the military after a president is elected. Many are concerned that the generals who took power after Mubarak's fall on Feb. 11, 2011, will try to retain influence.

The two days of voting, which end Thursday, are not expected to produce an outright winner among the 13 candidates vying for the post. If no one gets at least 50 percent of the vote, the top two finishers will go to a runoff June 16-17. The winner will be announced June 21.

The generals who took control after Mubarak was ousted have promised to hand over power by July 1, repeatedly assuring critics that they have no wish to remain in charge. There are fears, however, that they could retain significant powers on matters of national security and key foreign policies.

"I like the personality of Shafiq. He is strong enough to lift the country," said Suheir Abdel-Moamen, one of several women standing in line waiting to vote in the middle class Cairo district of el-Zawiya al-Hamra.Somaiya Imam, still undecided on who to vote for, replied with a reference to Islamist candidates, saying: "Don't you think we should vote for the candidate who holds the Quran?"

"We voted for them before and they let us down. They want everything - the presidency, parliament and government. They are never satisfied," Abdel-Moneim responded.

A woman standing behind the two chipped in: "But he (Shafiq) is a Mubarak's associate."

Sabahi, who adopts the socialist ideas of Egypt's late leader Gamal Abdel-Nasser, has been the choice of many who neither want an Islamist or a Mubaral-era figure for president. Others have turned to Abdel-Moneim Abolfotoh, who is an Islamist but is seen by some liberals as moderate enough.

In Cairo's northern Matariya district, a young IT specialist who asked not to be identified said she decided to vote for Sabahi as the middle-ground candidate.

"I wanted to vote for Ahmed Shafiq, because I am convinced he is the right man for the moment, but because I am afraid of what Islamists might do, I changed my mind and voted for Sabahi," she said. "Islamists either Salafis or Brotherhood are dying to hijack power. I am not going to give my vote for them."

Shafiq has been openly disparaging of the pro-democracy youth groups who led the 18-day uprising that forced Mubarak out of office 15 months ago. Critics accuse him of being too cozy with the generals who took over from Mubarak and whose own reputation is tainted by human rights abuses and authoritarian tendencies.

But with his strongman image, he has appealed to Egyptians who crave stability and fear Islamists.

Shafiq was met by several dozen protesters screaming "down with the feloul" as he arrived to vote in an upscale neighborhood east of Cairo on Wednesday afternoon. Some protesters showed their contempt by holding up their shoes in his direction. On his way out, some mobbed him, swinging their shoes at him as his security hustled him into his car.

> ___

Associated Press correspondent Aya Batrawy contributed to this report from Alexandria, Egypt.