The unexpected and sudden demise of Andrew Broad's political career because of a sex scandal has left the federal National Party without an obvious replacement and increasingly worried it is at risk of losing the safe seat in its heartland.

Key points: Andrew Broad's sudden political demise leaves the National Party without a replacement in his safe seat

Andrew Broad's sudden political demise leaves the National Party without a replacement in his safe seat Deputy leader and Victorian senator Bridget McKenzie touted as potential Nats candidate in Mallee

Deputy leader and Victorian senator Bridget McKenzie touted as potential Nats candidate in Mallee Sky News presenter Peta Credlin among the names the Liberal Party could pre-select for the seat

Potential candidates are beginning to emerge as a replacement for Mr Broad in the Victorian seat of Mallee, including the party's deputy leader Bridget McKenzie.

Prior to Mr Broad's election in 2013, just three men had held the seat, with an average tenure of more than 24 years.

The party expected Mr Broad would hold the seat for decades and his political demise has caught the National Party off-guard and without a succession plan.

Senior figures within the party have declared they would support Senator McKenzie, a cabinet minister who has represented Victoria in the Senate since 2011, if she runs in the seat.

When directly asked if she would nominate for pre-selection, Senator McKenzie would not be drawn, insisting it was a matter for the party's members in Mallee.

"I'm [a] senator for the great state of Victoria and am loving that role," she said.

But there are deep-seated fears within Victorian ranks that selecting Senator McKenzie, rather than someone who lives in the electorate, would but make retaining the seat difficult.

"Doesn't she live in Elwood?" several party members asked when Senator McKenzie's potential candidacy was raised.

Senator McKenzie's register of interests lists that she owns an investment property in Elwood, a wealthy and leafy suburb in Melbourne. Her previous declarations listed the Elwood property as her residence.

Since joining the Senate, her electorate office has been in Bendigo, in central Victoria, but Senator McKenzie recently announced she would relocate it to Wodonga, in the Lower House seat of Indi, amid speculation she would contest that seat in the future.

Senator McKenzie again confirmed that relocation despite the speculation she was considering running in Mallee.

"I'm moving my electorate office to Wodonga, which is at the opposite end to Mildura in the state of Victoria," she said.

"I'm very, very glad to be the senator for Victoria until 2021."

Another National Party figure said it would be "absolutely foolish and disrespectful to the electorate" to parachute someone into Mallee, and hoped a local woman would be chosen.

Mr Broad lived on a farm at Bridgewater, outside the Mallee electorate, when he first ran for the seat. He owned a property in electorate and lived in Mildura while serving as the MP.

Could Credlin run for the Libs?

Peta Credlin was born in regional Victoria and has been touted as a possible Liberal candidate. ( ABC News: Luke Stephenson )

Sky News presenter Peta Credlin, a former chief of staff to Tony Abbott when he was prime minister, was born in the electorate and has been touted as a possible Liberal Party candidate.

When asked on Sky News about potentially running in the seat for the Liberal Party, she failed to rule it out.

Though well known in political circles, few people the ABC spoke with in Mildura knew who Senator McKenzie or Ms Credlin were.

The Liberal Party last ran a candidate in Mallee in 2013, when Mr Broad was first elected.

He won the seat with a 6 per cent margin over Liberal Chris Crewther, who shifted back to the electorate to contest the seat.

Sources have estimated the Liberal Party spent about $750,000 in that battle but few expect that amount of money will be spent at the next election, with the party in a battle to retain crucial seats in Melbourne.

Sources expect a big field of independents will contest the seat and preference the Liberal Party as a protest against the National Party.

Deputy Prime Minister Michael McCormack said it was a matter for pre-selectors to decide the next candidate for Mallee, but that he would welcome a female being pre-selected.

"If Bridget decides that she's going to have a go at contesting Mallee, then she will have my full support," he said.

"The Nationals often look to a local champion. I'm sure there are plenty of local champions in and around Mallee and I have every confidence that the Nationals will choose the right person to contest that seat."

Sprawling conservative electorate

Mallee is a sprawling electorate that covers almost 82,0000 square kilometres, making it the 12th-largest electorate in the country.

Being a regional Victorian seat that has been long held by the Coalition, it has been increasingly compared to the seat of Indi, which independent Cathy McGowan won from the Liberal Party in 2013.

But Mallee is almost three times bigger in size, which political insiders say makes it harder for an independent to contest if they do not have a high profile already.

There are three major cities within Mallee — Mildura, Horsham and Swan Hill — which sit about three hours apart and have very different community profiles and media landscapes.

While an independent toppled a long-serving state National MP in Mildura in this year's state election, the win was just 253 votes.

The other two state seats that sit within Mallee — Lowan and Murray Plains — both featured swings to the incumbent National MPs.

Field of local women emerge as contenders

Andrew Broad will retire from politics amid a sex scandal that has suddenly ended his career. ( ABC News: Alexandra Beech )

Mr Broad was a former Victorian Farmers' Federation president — the youngest ever — and when elected at 38, many believed he had a job for life.

Given his age, many in the party expected it would help him weather accusations the Nationals were too old and stale.

A National politician told the ABC that they were confident, despite the loss of the Mildura state seat, the party remained popular within Mallee, especially in the more conservative, southern parts of the electorate prior to this week.

They now feared the response to Mr Broad's indiscretions would have "huge reputational damage" and were a "terrible look" for the party.

Party members and sources the ABC has spoken with largely agree a woman should be pre-selected — a move that would offer a stark contrast to Mr Broad.

"Bridget might be the first female leader if she's inclined to go for pre-selection," a Mallee party member told the ABC.

"I'd be wary of wasting a good candidate in that seat if I were them. Word on the street is [the Nationals Party] won't hold regardless."

Another party member said he expected independents would fare well, but was confident Senator McKenzie could win.

"Bridget McKenzie is a strong advocate for her constituents. I rate her and reckon she's a good operator," he said.

Other names to have been touted for the seat include former Citrus Australia boss Tania Chapman, Carolyn Walsh from the Birchip Cropping Group, Horsham councillor Pam Clarke and former Nationals candidate Anne Mansell, who has previously worked as a policy adviser for Mr Broad but now runs Dried Fruits Australia.

Nominations for National Party pre-selection will open on December 21 and close on January 4, with the candidate determined on January 19.