Liberal Democrat leadership candidate Tim Farron has said the Conservatives' £12bn (€17bn) welfare cut is proof of the moderating impact the party had as part of the previous coalition government.
Farron, who is competing against Norman Lamb to succeed Nick Clegg as leader, said the party hopped into bed with the Conservatives in the national interest, otherwise David Cameron would have probably won a second election later in 2010.
Defending the union, the Westmorland and Lonsdale MP told the BBC's Victoria Derbyshire that the party's legacy was becoming clearer after the Tories secured an outright majority at last month's general election.
"The last six weeks have proven that we made a massive difference," Farron said.
"We spent five years telling people we are stopping the Tories do 'X', we are making them do these things. Now it has taken the tragedy of our almost wipe-out on 7 May prove that we were right. We have seen the £12bn being taken out of welfare that we stopped."
Leadership opponent Lamb, MP for North Norfolk, said the party suffered at the ballot box because of some "stupid mistakes".
The former care minister said the party was left in the wake of the Conservative "machine" and, over tuition fees, added: "Once you lose the trust of people, they will stop listening to you."