A day earlier Sanchez, a Socialist, wrote on Facebook that he considered the plagiarism allegations a "personal attack" by opposition parties in the absence of a "solid political project." He also threatened to take legal action against ABC newspaper and other media that published stories arguing that passages of his "Spain's Economic Diplomacy, 2010-2012" dissertation had been copied from other researchers' works.
Doctored or exaggerated resumes have backfired in Spanish politics in the past, but academic misdeeds uncovered by the media have led to political turmoil and a string of high-profile resignations in recent months.
They include the conservative former president of the Madrid region and a health minister in Sanchez's cabinet, who both stepped down amid allegations that they had obtained master's degrees at the same private public policy institute in Madrid without apparently showing up for classes or by copying passages of their papers.
Courts in Madrid have opened an investigation and the Supreme Court is separately probing the degree obtained by the current opposition leader, the Popular Party's Pablo Casado, who graduated from the same university.
Media lined up at the library of Sanchez's alma mater in Madrid on Wednesday shortly after another opposition leader, Citizens' Albert Rivera, dared the prime minister to publish his thesis to dispel "reasonable doubts" over its existence. The journalists found a single printed copy that the university wouldn't allow to be copied, and also learned that Sanchez had not authorized online copies.
Amid mounting pressure, the thesis was finally uploaded on Friday to an Education Ministry online directory for academic researchers. The prime minister's office also issued a statement saying the thesis had passed plagiarism tests of two specialized pieces of software used by academics.
Sanchez surprised observers of Spanish politics in June when he succeeded in ousting his predecessor with a vote of no confidence. While he won early praise for leading a cabinet with a majority of women, opening ports to migrants and offering an olive branch to the strong separatist movement in Catalonia, a cabinet member resigned within a week of taking the oath after an undisclosed tax fine emerged.
Sanchez's minority government, with only 84 Socialist lawmakers in the 350-seat lower house of the parliament, has also been marred by erratic policies and increasing criticism, reversing decisions to accept migrants crossing from Morocco, to authorize a sex workers union and, just this week, to halt arm sales to Saudi Arabia.
He lost his second cabinet member on Tuesday when Health Minister Carmen Monton resigned over irregularities found in the way she obtained her master's degree, including chunks of the final thesis copied from websites and other works.
Monton's resignation, and Sanchez's move to publish his dissertation, seemed also aimed at exerting pressure on Casado, whose own degree is under investigation. The PP leader has said he doesn't fear the results of the probe.
A government spokeswoman said on Friday that both Casado and Rivera — whose official resume on the parliament's website had shrunk overnight — "should rise to the challenge" and respond with "transparency" to Sanchez's move. Isabel Celaa, who is also the Education Minister, said the scandal shouldn't stain the name of the country's higher education, stressing that it affects one single institution.