As DMK chief M Karunanidhi demonstrated on Tuesday, 'secularism' is the ultimate political brahmastra: with it, you can do whatever you want, and your dirty deeds will have a 'secular' legitimacy.

The shortest route from anywhere to anywhere else in Indian politics is through Secularism Avenue - as DMK president M Karunanidhi demonstrated on Tuesday.

Your entire political career may have been driven by the most vile caste-based identity politics, you may have given moral legitimacy to political assassins, your party may be monumentally corrupt, your daughter may have served prison term (and still face trial) on corruption charges, and even though you are a wheelchair-bound geriatric, you may need to perform agile gymnastic contortions to explain your political flip-flops.

But in the end, there is one 'brahmastra' that you can pull out to explain away your polygamous politics: you want to defend 'secularism', whatever that means.

Likewise for the Congress: it may have been caught with its hands in the till in the many corruption scandals that have come to define its term in office, the government it heads may have been reduced to a lame-duck, minority arrangement, it may have itself played the most perverse communal political games. But in the end, it can always count on its allies to bail it out by invoking the shibboleth of 'secularism'.

In that sense, 'secularism' is an 'invisibility cloak' worthy of Harry Potter. When you have it on, you can do whatever you want, and your dirty deeds will have a 'secular' legitimacy.

On Tuesday, Karunanidhi played his 'secular' trump card yet again to explain his decision to support the UPA government (of which his party, the DMK, is a constituent. The DMK opposes the contentious move to permit FDI in multi-brand retail, he said, but even so, it had decided to support the UPA government in Parliament on the issue solely in order to prevent "communal" forces from coming to power.

“When this discussion comes up in Parliament, though there may be thousands of differences (between the UPA and the DMK on the issue), thinking about the unfavourable incidents that may emerge if this government falls at the Centre, it has been decided to support the UPA with bitterness,” Karunanidhi said in a statement.

If anything happened to the UPA government, he added, it would only benefit the BJP. "We have to think of mosque demolitions, kar sevas, anti-minority measures and similar other communal atrocities if the BJP or a communal government it supports assumes power at the Centre," he added.

But beneath this seemingly high-minded charade, the reasons for Karunanidhi's doing back-flips to explain his political fecklessnes - in opposing the proposal for FDI in retail and yet voting for it - aren't hard to trace. His daughter Kanimozhi is still undergoing trial in the 2G scam cases, and to the extent that the Congress is still the puppet master that yanks the CBI's strings, it still determines the DMK's political destiny. The case against Kanimozhi,after all, will be only as good as the prosecution wants it to be.

Nor is Karunanidhi alone in invoking the 'secularism' card to bail out the Congress. Samajwadi Party leader Mulayam Singh Yadav too touted much the same reason when he stepped in after Trinamool Congress leader Mamata Banerjee withdrew support to the UPA government over the issue of FDI in retail and the diesel price hike.

Soon after Mamata Banerjee walked out, Samajwadi Party leader Ramgopal Yadav (who is Mulayam Singh’s brother) noted that although the Congress was guilty of a number of governance failures, the Samajwadi Party would perhaps have to step up and prop it up in the interest of stopping the BJP.

“This government would have fallen long ago. Many parties share our view on it (corruption, price rise and unilateralism in alliance). But we cannot forget the Gujarat riots and how the state sponsored them. We have seen that face of the BJP. So, we have to think twice before taking a step lest it helps such forces in coming to power,” Yadav had said at that time.

But such specious reasoning notwithstanding, the Karunanidhi's and the Samajwadi Party’s alibi for their stated intention to bail out the government merely reflects the debasement of political posturing in India, where anything – including monumental corruption, such as the UPA government has overseen in the past three years – can be defended in the name of upholding “secularism” as defined by opportunistic invocations of that slogan.

Like Karunanidhi, Mulayam Singh too is susceptible to political blackmail - to the extent that he too faces charges of having acquired assets disproportionate to his known sources of income. The Congress has the capacity to abuse its power and taint him - or allow him to walk free.

But the cynical politics of playing the 'secularism' card may be close to its sell-by date. The taint of being seen to be joined at the hip, in the way that the Congress and the DMK are (as coalition allies), will recoil on both of them - in the way that it did during the 2011 Assembly election in Tamil Nadu. Which is perhaps why neither of them can stand the stench emanating from the other, but gamely march, hand in hand, down Secularism Avenue - in the hope that their 'invisibility cloak' will mask their perverse politics. But when their magical cloak loses its invisibility powers, their naked politics will be on glorious display for the world to see.