The Scottish Liberal Democrat leader compared the situation with Theresa May’s beleaguered attempts to negotiate a Brexit deal amid various demands from factions within her Conservative Party.
Speaking to the PA news agency, Mr Rennie said the last decade of Scottish politics has been “bedevilled” by arguments about the constitution and fears about the prospect of five more years of nationalist infighting, unless the SNP can be deprived of a majority.
He said he believed the SNP’s plan for another independence referendum by 2023 would be derailed if they fail to get an overall majority on May 6, and argued that parliament could instead focus on a recovery from the impact of the coronavirus pandemic.
Mr Rennie said: “If the SNP, the nationalists, get a majority, I think Nicola will have a whole host of back-seat drivers.
“She’s lost control of the nationalist movement already and I think there will be people shouting out all the time from the back seat telling her exactly which direction to go in and she’ll be beholden to them because she’ll have your commitment to try and pursue this whole independence agenda.
“But they don’t agree with each other – Alex Salmond wants it on day one, he’s talking about taking to the streets.
“I don’t quite know what the Greens’ strategy is, but we know they changed their strategy a few weeks after the last election, so who knows what they’ll do this time, and there’s not one single view within the SNP about how this should be done.
“Nicola keeps pushing it back and who knows where it will end up.
“She’s almost beginning to look a bit like Theresa May who, despite her best efforts, she’s got a factionalised movement behind her that’s pulling in all sorts of directions, and is trying to control things from the back seat.”
He added: “If we turn back from that and make sure that they don’t get that majority, then there’s a real chance we can get the parliament focused on recovery.
“That’s the choice we’ve got.
“We’ve got Nicola driving the vehicle as a majority, with all these back-seat drivers telling her where to go.
“Or we can have a parliament that is resolutely focused, working in partnership to get recovery put first and to create jobs and tackle climate emergency and make sure the NHS is back up to speed, and cutting waits for mental health treatment and make sure we’ve got bounce-back support for education.
“If we can do all of those things that would be, I think, providing a service in the country that I think the last 10 years hasn’t because we’ve been bedevilled by the constitutional arguments.”
Maree Todd, the SNP’s Caithness, Sutherland & Ross candidate, said: “The Lib Dems will say just about anything to try and stay relevant.
“While opposition parties obsess over which one has the most Trump-like undemocratic stance on the constitution, the SNP is focused on getting Scotland through and out of the pandemic, and delivering for the people of Scotland.
“The SNP is the only party with credible and progressive policies to support people and businesses, including removing business rates for retail and hospitality for 12 months, bringing forward plans to tackle child poverty, invest in our NHS, build more affordable housing, abolish dental charges, and deliver free school meals for all primary pupils.
“Only both votes SNP will deliver an SNP government with transformative policies for a strong, fair and green recovery, and put Scotland’s future in Scotland’s hands in a post-pandemic referendum.”