It’s worth remembering that polling gaps really do narrow when election campaigns start. We all remember the 2002 campaign. Labour reached 53% support in April; on Election Day in July, they polled 41%. The gap between labour and National had been blowing out to 30% in the polls but in the end it was less than 20%.
Take a look at what happened to Labor and the Coalition’s support in Australia last year. Once the campaign began the gap narrowed from over 20% to less than 5% on Election Day.
If National is only ahead of Labour by 5% on Election Day, John Key’s ambitions for his CV are toast.
[note the polls are evenly spaced on the graph but there were more frequent polls after the campaign proper started, so the narrowing of the gap is more sudden that it appears. Labor lost 16% of lead in just 40 days]