The transition in Sinn Fein leadership with Gerry Adams stepping down and Martin McGuinness tragically passing away is causing whiplash for many observers so used to decades of continuity in the Sinn Fein top jobs.

Adams and McGuinness seem certain to be replaced by Michelle O'Neill, already in situ in the North, and Mary Lou McDonald in the south. Two younger, articulate women have replaced the hardened revolutionaries of the early struggle. It is a massive sea change, expertly managed to date.

Sinn Fein's future, Mary Lou McDonald and Michelle O'Neill.

Sinn Fein's future, Mary Lou McDonald and Michelle O'Neill.

The new leadership gives relevance to Sinn Fein’s efforts to attract the younger, less committed voter.

Sinn Fein in the opinion polls

Opinion polls show Sinn Fein is the most supported party among voters under 40 in the Irish Republic. Keeping the loyalty of such voters as they age is critical to Sinn Fein’s leap to power.

The opinion polls also show Sinn Fein anchored in the mid-teens to low 20s in overall support, with Fianna Fail and Fine Gael in the mid-twenties. Sinn Fein would make the obvious coalition partner for either party, although both Fianna Fail and Fine Gael deny they will ever share power with them.

McDonald’s task will be to drive those numbers closer to the other two parties and eventually pass them. It is a tall order, but it is not that long since Sinn Fein were down around 2 per cent support. They are also known for playing the long game.

Gerry Adams, walking behind Sinn Fein's Conor Murray and Mary Lou McDonald at the 2017 Ard Fheis.

Gerry Adams, walking behind Sinn Fein's Conor Murray and Mary Lou McDonald at the 2017 Ard Fheis.

In Mary Lou McDonald they would choose wisely, though they have no shortage of young talent in their ranks.

At 48 she fits the age and region profile – from Dublin, convent-educated, graduate, solid middle class, was originally in Fianna Fail before plumping for Sinn Fein.

She also addresses Sinn Fein’s most critical constituency – middle class women who are turned off by the whiff of cordite from the party’s old IRA links.

Read more: Gerry Adams to step down - made a united Ireland a major issue again

Brexit's impact on Ireland

In person she is affable, good with people and can explain complex issues very plainly. She is particularly impressive on the issue of Brexit which will be a huge part of the next leader's profile.

Sinn Fein's Mary Lou McDonald TD meets with Senator Elizabeth Warren on the Brexit vote and the consequences for Ireland.

Sinn Fein's Mary Lou McDonald TD meets with Senator Elizabeth Warren on the Brexit vote and the consequences for Ireland.

Like Adams she is dogged. She polled poorly in Dublin Central the first time she ran, but two elections later she topped the poll and in the interim, was elected to the European Parliament, where she came close to being named European MP of the Year.

She is concise on a united Ireland and the impact of Brexit.

She spoke of how high the Brexit stakes are in a talk at the Magill Summer School last summer. She stated: "Brexit has created a constitutional earthquake and its aftershocks have exposed the fault lines of partition in Ireland.”

She said the border was now exposed as the “false construct it has always been” and that its contradictions must now be dealt with.

“Partition has failed the test of time. Yet some tell us that the time is not right to talk about unity. Now is the time to plan for unity, to build support for unity, to challenge division, and build an Ireland for all our people.”

It is such straight talk and directness that boosted her to the role of obvious successor to Gerry Adams. They are massive shoes to fill, but she will hardly change her style of constant engagement with governments and rivals. Beneath the quick smile and laugh there is a steel that has brought her to the cusp of leading Ireland’s fastest rising political party. Someday it could install her in the office of Taoiseach.

Read more: Sinn Fein raises $400,000 at NYC dinner, Adams announces new unity drive in US

Here is Mary Lou McDonald speaking at this weekend’s Sinn Fein Ard Fheis:

Gerry Adams, Michelle O'Neill and Mary Lou McDonald at the 2017 Sinn Fein Ard Fheis.RollingNews