The parliamentary debate arrived after a frantic weekend of talks by Pedro Sánchez's Socialists with the far-left United We Can party to strike a last-minute deal to create a coalition government.
"I propose a government that is progressive, that protects the environment, that furthers women's rights and that strengthens Europe," Sánchez told the Madrid-based Congress of Deputies, the lower house of parliament.
But after outlining a battery of policies aimed primarily at combating unemployment, the impacts of climate change and the new digital economy, and improving education, Sánchez waited to the very end of his two-hour speech to include a short message aimed at United We Can.
"We have seen that it is not easy for us to reach an agreement," Sánchez told United We Can's parliament members.
"(But) it is up to us to keep working and see this through. And then we will have the opportunity to move forward with that which unites us, which are the promises of the left, a society of men and women living in harmony with nature."
Sánchez's Socialists won the April 28 general election with 123 seats but he still needs the support of United We Can's 42 seats and other smaller parties to stay in power.
After weeks of stalled negotiations between Sánchez and United We Can, on Friday the deadlock was broken when United We Can leader Pablo Iglesias accepted the Socialists' condition that he couldn't form part of a new Cabinet. That sparked a rushed series of talks and optimistic messages by the Socialists that a deal is possible.
But 24 hours before his first of two tries to win the backing of a government, and the deal isn't done.
The pony-tailed Iglesias glumly listened to Sánchez's speech slouched in his seat.
On Tuesday, Sánchez needs to get an absolute majority of 176 of the 350 parliament members. If he fails on that first bid, the bar lowers on Thursday, when he just needs more "Yes" than "No" votes.
If he fails on both attempts, a two-month countdown starts for Spain to form a government or new elections would be triggered.
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