Hillary Clinton made it official on Sunday and it seems certain a smooth path to the Democratic nomination awaits.

But what if there is a massive upset? Where would it come from?

Hillary Clinton aides point to former Maryland governor Martin O’Malley as the obvious alternative to her for the Democratic nomination and her most serious challenger says Politico Magazine.

He is also a front-runner for Vice President on a Hillary ticket if circumstances work out that way. It is a fraught path while he runs against Hillary but not an impossible outcome by any means -- one that would be enormously popular in Irish American circles.

The former Maryland governor will announce his own presidential bid in May insiders believe, setting up the ultimate David vs Goliath contest.

He had the perfect chance to opt out of the uphill race when Senator Barbara Mikulski stepped down and an unexpected Senate seat became available in Maryland.

He never even considered it despite friends urging him to.

He has already been ploughing the furrows in Iowa and New Hampshire and supporters say there is a solid and committed group of enthused voters there, mostly the “anyone but Hillary crowd.”

By mid to late May they are gambling the bloom will have come off the Clinton rose and the media hype will have subsided and Democrats will be ready to hear from a candidate to the left of the front-runner. O’Malley will then make his move.

O’Malley is actually on good terms with the Clintons. He was one of the few Democratic governors who stayed with Hillary until the bitter end in 2008 when most others jumped and swam to the all conquering battleship Obama.

He goes back 25 years with them. Back in 1995 I was his seatmate on the American delegation as we went to Northern Ireland on President Bill Clinton's first trip there, a moment of great history.

O'Malley was then Baltimore mayor, but it was his knowledge of Irish history and politics that really stayed with me.

Unlike most politicians with an Irish name, he had actually dug deeply into his heritage and history and there is hardly an Irish issue, either historically or present day, he is not knowledgeable about.

He attended the American Ireland Fund annual Irish weekend in Kildare two years ago and was deeply impressive on Irish topics.

But what makes him think he can topple the astonishing odds against him?

One thing to know is that rivals ignore O’Malley at their peril. Most of the jobs he's run for – city council, mayor, governor – he started out as long odds against but pulled off remarkable victories.

Now with two successful terms as Maryland governor behind him (he left office with high approval numbers) he believes he has enough political weight to make it a contest.

At 52, handsome, Irish with an accomplished wife and handsome family, the Kennedy-like vibe is very obvious and one he will do nothing to discourage.

He’s already played the White House -- literally. In 2013 he and his band O'Malley's March were the musical entertainment on St. Patrick’s night as Obama entertained the visiting Irish leader Enda Kenny. What was even more interesting was how he worked the rooms full of top American political figures afterwards.

As head of the Democratic Governors Association, a post once filled by Bill Clinton, he made invaluable contacts.

When the White House campaign begins in earnest he knows there is at least 30 percent of the Democratic primary voters who pine for Elizabeth Warren and could well switch their allegiance to him as well as a slew of media who will promote anyone but Clinton.

He also knows that change is the most powerful dynamic and important word in Americans politics and whatever her extraordinary accomplishments, Hillary Clinton cannot embody that word.

He can do that and has already made it clear that he sees openings among voters who are tired of the Clinton/Bush dynasty dynamic.

Behind the musician and hail fellow well met is a razor sharp policy wonk who likes nothing better than a down-in-the-weeds discussion on public policy and how systems and governments can work better.

He will excel in debates and hopes to catch fire like Obama did in 2008. The comparison is hardly apt, however. Hillary Clinton has a massive lead and very deep pockets, but O'Malley will relish the Irish underdog role.

Besides, there is always the potential of topping the VP list – an Irish Catholic choice to bolster Pennsylvania and Ohio as Obama made with Biden.

His thinking is clear. Why not have a go at the big prize? He knows that back in 1990 in the run up to the 1992 race a similarly unknown young governor called Bill Clinton seemed an afterthought with New York governor Mario Cuomo a shoo-in for the Democratic nomination.

Then Cuomo pulled out and history was made. O’Malley will be hoping something similar can happen again. Even as a VP on a Hillary ticket it would be a powerful boost for Irish America.

Martin O'Malley and Hillary Clinton photographed in 2008 during her campaign for presidency.Associated Press