Having a belligerent, nuclear-armed neighbor is one hell of a campaign issue, but even by that measure, 2017 is unusual.

On May 9, South Koreans will choose a replacement for impeached President Park Geun-hye , who was removed from office in March and indicted on charges of bribery and abuse of power last month

As voters mull their decision, Pyongyang is believed to be prepping a sixth nuclear test, and has conducted multiple missile tests, while US President Donald Trump's unpredictable White House has talked of a potential pre-emptive strike that some fear could lead to a second Korean War.

Park's administration took a hardline on North Korea, but if Democratic Party frontrunner Moon Jae-in wins next Tuesday's vote, South Korea's Pyongyang policy is about to change.

South Korean presidential candidate Moon Jae-in is expected to take the country in a new direction on North Korea if he wins Tuesday's election.

Return to Sunshine Policy?

During the campaign, Moon has pushed for a more open approach to North Korea, which would combine negotiation and economic cooperation with military and security measures.

"I am confident to lead the diplomatic efforts involving multiple parties, which will lead to the complete abandonment of the North Korean nuclear program, and bring the relationship between South and North to peace, economic cooperation and mutual prosperity," he said in an April 25 debate.

Sunshine Policy Foreign policy of South Korea from 1998 to 2008

Policy of engagement with North Korea on economic and political issues

Two South Korean Presidents traveled to Pyongyang

Earned South Korean President Kim Dae-jung a Nobel Peace Prize

Fewer North Korean nuclear and missile tests during this period

Ultimately failed to stop North Korean nuclear program

Open communication with the North Korean regime stands in stark contrast to the previous nine years of conservative policy, which advocated a hardline approach and tough sanctions as punishment for Pyongyang's pursuance of nuclear weapons.

Moon's views are seen by many as a throwback to the Sunshine Policy of the liberal governments of 1998 to 2008; no surprise, as he was a key adviser to those administrations.

During the Sunshine Policy, Seoul actively engaged Pyongyang, which led to closer relations on both sides of the border and saw two South Korean Presidents visit the North Korean capital. However, the approach ultimately failed to halt North Korea's nuclear weapons program.

Michael Breen, author of "The New Koreans," said Moon favors strong defense and "engagement with North Korea with realistic expectations."

"That's something a lot of people can live with," he said.

Park's shadow cast over vote

While conservatives have predictably denounced Moon, his North Korea policy doesn't seem to be turning off prospective voters.

A former human rights lawyer and special forces soldier, he is leading the final round of polls by more than 18 points.

Moon's main rival, the centrist software mogul Ahn Cheol-soo, has declined steadily in the polls after a series of disappointing debate performances.

And while Moon has been attacked for allegedly being soft on North Korea, his popularity arises from the corruption scandal that took down Park, said Yonsei University professor John Delury.

"The electorate wants to punish the whole party for the misrule of the Park era," Delury said.

He said voters are still angry over the accusations of collusion between business and political interests and they see Moon as a "clean" candidate.

Hong Jun-pyo, who is standing for Park's Saenuri Party -- since rebranded as Liberty Korea Party -- is polling at around 16%, according to the latest figures.

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Path to peace treaty?

While Moon's popularity may come from his stance on reform and tackling corruption, his critics have tended to focus on his stance toward Pyongyang.

"Moon struggles to prove allegiance to South, not North," read a recent headline in South Korea's Yonhap News Agency, and at times during debates he has come off as defensive on the issue, repeatedly saying that negotiations exist as a tool to persuade North Korea to give up its nuclear weapons.

During the campaign, Moon has laid out a multi-layered approach to North Korea including expanding several defensive military programs, but also "signing a peace treaty in the Korean Peninsula after the nuclear issue has been completely resolved" and restarting economic cooperation including on tourism sites, joint industrial zones and aid.

Such measures have not historically been popular with conservative administrations in the US. As a result, Moon's success may depend as much on Washington's response as Pyongyang, Delury said. He added, it's "tough to tell" how hard the Trump administration would work to block any new initiative from Seoul.

The two countries have a decades-long military and political alliance dating back to the Korean War. More than 29,000 US troops are stationed in South Korea, and both countries are treaty-bound to guarantee the other's defense.

While Republican US administrations have typically taken a hard line on North Korean issues regardless of their counterparts in Seoul, this week Trump injected more uncertainty into US policy when he said he would be "honored" to meet leader Kim Jong Un under the "right circumstances."

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US relationship

Moon has played up Trump's apparent willingness to sit down with Kim, telling the Washington Post that he is on the "same page" as the US leader on the issue.

"I believe President Trump is more reasonable than he is generally perceived. President Trump uses strong rhetoric towards North Korea but, during the election campaign, he also said he could talk over a burger with Kim Jong Un," Moon told the newspaper.

However, one area where they are definitely not in agreement is over the deployment in South Korea of the US Terminal High Altitude Area Defense (THAAD) missile defense system.

This week, Washington and the caretaker government in Seoul announced THAAD was up and running , at least partially. Moon has opposed the THAAD deployment and called for the matter to be decided by the next South Korean government following public consultation and a vote in the National Assembly.

Breen said the deployment is likely now a done deal, but the process has upset some in Seoul.

"It's touching a nerve here, which everyone can relate to, the US disrespecting South Korean sovereignty," he said.

Euan Graham, a Korea expert at Australia's Lowy Institute, said the THAAD deployment and Trump's rhetoric about Korean issues risks "inflaming a sense that (the country) is being bypassed on its own national security concerns."

Fears that the US could "go it alone" on North Korea -- to use Trump's own words -- have cast a shadow over the election.

Moon said in an April 13 debate that if something like another North Korean nuclear test happens and the US plans a military response, his first call isn't to Pyongyang, but to Washington, to tell Trump not to strike without South Korean agreement.