Calum Higgins, Labour's great hope for Carmarthen East and Dinefwr, was wheeled out by Labour's spin doctors to front one such attack on Plaid this week.
Leanne Wood had said that Plaid Cymru would not prop up a minority Tory government after the next election.
Perhaps they might, said Calum. They haven't ruled it out, huffed Calum (or whoever was writing the script). They are totally discredited, puffed Calum. And much more of the same as he ranted for several paragraphs about nationalists.
In the middle of this, Calum did what Labour has been careful to avoid doing - he mentioned Ukip. Specifically, he suggested that Plaid Cymru needed to worry about Ukip.
A few days after Calum had conveyed the thoughts of Labour HQ to the Western Mail, Labour slumped to third place in the Rochester by election and saw its vote halved. Until the 2010 general election the seat had been held for Labour by Bob Marshall Andrews (on slightly different boundaries).
In his victory speech, Mark Reckless made it clear that he and Ukip would now be going after the Labour vote.
Back home, Calum will remember that in May of this year Labour came third in the poll for the European elections in Carmarthenshire, with Plaid in first place and Ukip in second.
Labour has been incredibly slow to wake up to Ukip, probably because it believed that this was just a turf war between two parties on the right and that Labour would benefit as a result. So Labour's response has been to keep quiet while joining in the arms war of proposals to crack down on foreigners.
Let's employ loads more border guards. Let's charge foreigners who want to come to Britain. Let's find ever dafter ways of targeting one-legged Bulgarians and Polish plumbers, even though all the evidence shows that European migrants contribute more in taxes and take out less in benefits than holders of UK passports.
There is a long history of this in Britain. A hundred years ago popular newspapers were reporting that Russians had been seen in central London with snow on their boots. There were anti-German pogroms in the First World War, with attacks on people who were suspected, often wrongly, of being German.
In one of the poshest parts of London German Street was renamed Jermyn Street. A change of spelling made everything all right.
In the 1950s and 1960s landlords would advertise rooms for rent, but "No Irish, No Blacks, No Dogs". Last night a woman wearing a Ukip rosette in Rochester was interviewed for the main BBC evening news bulletin. "I am a Dutch Canadian", she proudly told viewers, before going on to warn of the dangers of immigration.
Two weeks ago I met a couple who had moved to Wales from a prosperous cathedral city in England. Mr J was originally from the Valleys, but decades of living in England had left him with only a faint trace of an accent. Judging from her accent, Mrs J was originally from London. They had moved to west Wales because they no longer felt comfortable in the city they had lived in for many years and had been subjected to abuse.
The area they had lived in had many Asian Muslim residents, Mrs J said, but they were friendly and had not been a problem.
Nasty, anonymous notes had been posted through their letter box, and Mr J had been openly abused by a white woman on the street who had yelled into his face, "You f***ing Welsh, coming here and taking our jobs".
"He's 83, he's not taking anybody's job", Mrs J said.
All of which brings us to Emily Thornberry, the now disgraced Labour MP who tweeted a "disrespectful" picture of a house festooned with England flags and the words "Image from #Rochester".
Ed Miliband was incandescent with rage, and Labour bigwigs queued up to apologise for the outrage. The owner of the flags was just being patriotic, they said, and he appeared, shaven headed, before the cameras with lots of Sun stickers plastered on his white van.
For all we know, this patriotic Rochester resident is into contemporary dance and going to Polish evening classes, but the flags, the shaven head and the Sun stickers would suggest otherwise.
We don't actually know what Emily Thornberry thought about all of this either because she posted the picture without comment, although we can probably assume that she was pointing out the rise of nasty, xenophobic right-wing nationalism in England.
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But for Calum and the Labour establishment, the sort of people who vote for the progressive, left of centre Plaid Cymru and the SNP are rabid nationalists of the worst kind, to which anything, even Ukip, would be preferable.
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