Hung parliament and the economy
Plaid Cymru's stance against the Conservatives in this campaign was always going to leave it vulnerable to the claim that, when push comes to shove, Labour will always be able to rely on its support.
After all, when you've made blocking a return for the Tories an absolute priority, then where else do you go?
The comments on the weekend by Leanne Wood that Plaid may withhold its support for Ed Miliband if he leads a minority Labour government are a way of trying to deal with that.
At the very least it sends out the message that it can't be taken for granted.
Plaid's problem is it that it doesn't spell out what the alternatives are if it doesn't support Labour.
Unsurprisingly, Labour has been more than happy to try to answer that question by saying it opens the door to a return for the Conservatives, which is explicitly what Plaid has been campaigning against in recent weeks.
Of course all of this only becomes relevant in the event of a hung parliament, which is exactly what the polls are suggesting will happen.
Despite what the Tories say about the NHS being the main doorstep issue and UKIP saying it's immigration, it is who is trusted on the economy that will decide who gets into Number 10.
And when it comes to the economy, a feature of the campaign so far is the striking contrast in the way the parties are describing the situation in Wales.
On opposite ends of the spectrum are David Cameron saying there's a jobs miracle underway while Labour and Plaid paint a picture of thousands of people using food banks, claiming what they call the bedroom tax or are on a zero hours contract.
What's the truth? The Conservatives say the truth lies in the stats and there were plenty thrown at journalists at the launch of their Welsh manifesto on Friday at the Royal Welsh showground in Builth Wells.
The event coincided with the latest unemployment figures, showing 12,000 fewer people unemployed on the quarter.
Behind the scenes I was being urged to make sure those figures were reflected in our news bulletins on the day.
Conservatives are acutely aware of the dangers of this being a vote-less recovery, or as Plaid one described it a "spreadsheet" recovery.
In other words, it's an economic recovery that is not being felt on the ground, which is the central claim of Labour.
The economy is the prism for all of the parties. The Liberal Democrats have for the first time based their entire campaign on the prospect of being a moderating coalition partner which would ensure the economy is not jeopardised by too much, or too little, austerity.
And UKIP claims that the British economy would perform better if it was freed from the shackles of being a member of the EU.
I'm not telling anyone anything new by saying it's down to the economy. How the parties turn it to their advantage? Well that's another matter.