Sonia Gandhi, other party leaders march to Manmohan Singh's residence in solidarity.

A day after former Prime Minister Manmohan Singh was summoned in the coal scam case, the Congress went on the offensive.

Party president Sonia Gandhi, accompanied by Congress Working Committee members and party MPs, marched in solidarity to Dr. Singh’s residence.

If this gesture of solidarity with Dr. Singh was a political act that galvanised the party on Thursday, the next step, party sources told The Hindu, would be the legal fight — to challenge the summons in the Supreme Court. This decision comes in the wake of consultations in the party with a battery of legal luminaries who are studying the 75-page court order.

It is learnt that former Union Minister Kapil Sibal will be the lead lawyer in the case for Dr. Singh. Indeed, on Wednesday evening, he not only had a session with Dr. Singh, he was also among those who were called for a closed door meeting with the Congress president: the others present included Congress leader in the Lok Sabha, Mallikarjuna Kharge, the Leader of the Opposition in the Rajya Sabha, Ghulam Nabi Azad, and former Union Minister Ashwini Kumar. It was also on Wednesday evening that Ms. Gandhi took the decision to lead top party leaders to Dr. Singh’s residence.

Former Union Minister P. Chidambaram — also a top lawyer — said in a statement: “The CBI, after recording Dr. Singh’s statement, concluded that there were no grounds to initiate criminal proceedings against him. We respect our judicial system, we respect our judges. But I may point out that, in the past, Courts have taken a misstep and stumbled. I am confident … the Court itself will review its decision and drop the proceedings against Dr. Singh.”

Party sources added that Thursday’s protest may be followed up by a march to Rashtrapati Bhavan in the next few days. State units of the party are also likely to pass resolutions in support of Dr. Singh. On Thursday, reports came in from Uttar Pradesh of Congress workers stopping trains to register their anger.

Party leaders who reached Dr. Singh’s residence were greeted by the former Prime Minister and his wife, Gursharan Kaur. In a short meeting, Ms. Gandhi emphasised the need to support Dr. Singh with all the resources at their command; in turn, he thanked Ms. Gandhi and the party for their faith in him.

Earlier, addressing journalists, Ms. Gandhi stressed the party's “unstinted support” for Dr. Singh. “We will fight this legally with all the means at our command. I am sure we will be vindicated.”

Mr. Kumar told The Hindu: “We are studying the order and even on a first reading there appears to be gaping illegal irregularities. Despite the CBI saying there is no prosecutable evidence, such an order has been passed. This itself is a major ground for challenging the order.”

Interestingly, former Union Law Minister M. Veerappa Moily described the summons to Dr. Singh as reflective of a “crisis of law for this country,” something senior BJP leaders had said on Wednesday off the record.

The BJP is still not questioning Dr. Singh’s integrity, but has far more sharply trained its guns on the Congress. Parliamentary Affairs Minister M. Venkaiah Naidu told journalists: “We are not questioning Dr. Singh’s integrity but the Congress must take responsibility for what happened.”

Congress president Sonia Gandhi says party will fight allegations against former PM Manmohan Singh in >#CoalScam case legally >@the_hindu — Delhi Connect (@DelhiConnect) >March 12, 2015