But after an amazing Northern Ireland Assembly election result in the constituency in March, Sinn Féin can see the summit.
The party began 155 votes behind the SDLP on the previous assembly poll result of May 2016.
They emerged 6,650 votes ahead.
That is why many believe Chris Hazzard, one of Sinn Féin's two candidates in that election, is set to become the party's first MP for South Down.
But there is a caveat - or two.
Firstly, the SDLP's Margaret Ritchie easily beat Mr Hazzard in the 2015 general election - the margin was 5,891 votes.
And, of course, there is the old claim that in Westminster elections many unionists lend their votes to the SDLP to ensure Sinn Féin is defeated.
Right? Well, maybe not this time.
According to Paul Smyington, the editor of the Down Recorder newspaper, unionists who were spooked by the surge for Sinn Féin in March are telling voters on the doorsteps to "vote for the union".
He claims that could have an "important impact on this election".
Not that Ms Ritchie appeared bothered about the unionist factor two years ago.
In her victory speech, she told her supporters: "Let us be very clear that the SDLP vote increased and that we have a solid majority now in South Down without any votes being lent to us.
"So, let's lose that myth now."
That claim is about to be put to the test.
Asked about the forthcoming election, the outgoing SDLP MP chose her words carefully.
"I, as an MP who has served for the last seven years, have been an MP for all of the constituents in South Down, representing them on a wide range of issues," she said.
"Every vote is valued for me and I look forward to many, many people right across the constituency - irrespective of political affiliations - voting for Margaret Ritchie on 8 June.
"They will get an MP who will represent them both here in the constituency and at Westminster 24-7, 365 days per year."
Sinn Féin has been putting a massive effort into the constituency.
About 400 people, including the party president Gerry Adams, attended Mr Hazzard's campaign launch in Newcastle.
"When the results were coming in in March more people joined Sinn Féin in the six hours during the count than had previously joined in the previous six months in South Down," said Mr Hazzard.
"There's an appetite now for Sinn Féin that is growing year-on-year.
"We have canvas teams out in nearly every village and town every night and certainly the message coming back is positive.
"People see the work that we are doing, the leadership that we are giving and they're coming on board."
The largest unionist party, the Democratic Unionist Party, is not represented this time by the well-known Jim Wells but by a first-timer, 32-year-old accountant Diane Forsythe.
She said the election in March was a wake-up call for unionists.
"There's definitely that strong feeling that I'm getting on the doors that people are wanting to come out and put their pro-union support on the ticket," she said.
"I would ask them to do that because ultimately lending their vote to any nationalist party is a vote against the union."
Ulster Unionist Harold McKee, who lost his assembly seat in March, said the unionist mindset this time is difficult to read.
"I'm hearing mixed views on it," he said.
"I am a unionist and if I stand as a unionist I'll not be asking someone else to vote for another party - I expect them to vote for me."
The Alliance Party shocked many by out-polling the Ulster Unionists in March.
It is represented this time by councillor Andrew McMurray, who said the party has a "solid base".
"I think the positive, progressive and pro-European messages that we're putting out will hopefully resonate with the voters and they will show that South Down wants that Alliance voice."
Sinn Féin knows that Ms Ritchie cannot be written off.
But coming so soon after the assembly election and the Sinn Féin surge she will have to fight harder than ever if the SDLP's winning streak in South Down is to continue.
For three decades the chances of toppling the SDLP in South Down have been about as strong as the prospect of anyone scaling the Mourne mountains barefoot.