(Bloomberg) -- President Joe Biden is meeting Tuesday with Senator Kyrsten Sinema, the lead Democratic negotiator in the infrastructure talks, as bipartisan discussions on the $579 billion plan hit snags.

The Arizona senator is heading to the White House, according to people familiar with the matter, as Democrats and Republicans have been unable to resolve differences over transit funding, spending levels on water projects, whether all federally-backed projects should pay so-called prevailing wages and how much unspent Covid-19 money can be used to pay for infrastructure, among other disputed items.

Sinema and Biden will discuss the recent negotiations and how close they are to wrapping up, according to one person, who asked for anonymity because the meeting isn’t public. Politico reported earlier that Sinema would meet with the president.

Her Republican counterpart, Ohio Senator Rob Portman, also has been involved in talks with White House officials.

The negotiations have blown past several deadlines for reaching a deal, despite persistent expressions of optimism from lawmakers in both parties that they were close to an agreement. Senate Majority Leader Chuck Schumer of New York has warned that he’ll keep the Senate in session through the weekend if necessary.

“There will always, always be details that have to be worked out, but I’m pretty optimistic at this stage,” Utah Republican Senator Mitt Romney, a member of the bipartisan group, said. “Nothing’s 100%, but it looks pretty good.”

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