The party’s Westminster leader said that independence is now “closer then ever” and pledged launch a campaign targeting undecided Scots “right now” if he wins the battle to become Nicola Sturgeon’s No2.
And he believes Scots may find themselves voting in “short period of time” in another independence referendum.
He denied suggestions the SNP’s White Paper blueprint painted too rosy a picture of independence in 2014 but said an “appropriate case” would be needed for the current circumstances.
The Moray MP is pitching himself as the candidate of experience in the four-way contest to replace Stewart Hosie, who quit after newspaper disclosures about an affair.
He was pressed on whether he agreed with party colleague George Kerevan MP that Scotland could face five years of spending cuts in the event of a Yes vote during an interview on BBC Radio Scotland’s Good Morning Scotland programme on the final day for nominations for the depute leader post.
Mr Robertson said: “I don’t share all of George Kerevan’s analysis but, of course, I think it is incumbent on politicians of all political persuasions to say that not everything is going to be easy and, of course, establishing a sovereign state is a big step, and I think we need to be clear with the electorate and that’s why part of my pitch in this SNP depute leadership election campaign is that I think we need to be outward-focused.
“We shouldn’t be relying on the 45% of people who decided in favour of independence in 2014, we need to be aiming at the 100% of voters in Scotland, and particularly those 55% of voters who were not convinced.
“For some of them, the reason why they weren’t convinced was they thought that the explanation of why independence was a good thing didn’t concede that there were potential downsides and, of course, if one takes responsibility for oneselves it is entirely possible that one makes bad decisions, that there are downsides to things.”
He added: “I thought the White Paper was an excellent prospectus for the 2014 referendum but if and when we come to having to make a renewed decision on the basis of protecting Scotland’s place in Europe, I think we’re going to have to make the appropriate case for the time in which we find ourselves.”
SNP activists are due to debate a second independence referendum at the party’s conference in Glasgow later this year.
Mr Robertson said: “Since 2014 our membership has gone through the roof, there’s more than 120,000 SNP members now and we’ve got to do everything that we can to help enthuse and engage all of those members as the prospects for independence are frankly closer than they have ever been.”
He said he did not accept that there would be SNP voters who voted Yes in 2014 who might switch to No as they would not want to be part of the EU.
The MP said: “It is true, yes, SNP members did vote to leave the European Union but I think when the choice is presented, as I believe it is possible that it will be within a short period of time, that people would prefer the option of Scotland being a sovereign state, being able to decide on its future course of action.”
The other candidates standing for depute leader are MEP Alyn Smith, MP Tommy Sheppard and councillor Christopher McEleny.