Update: Trump announced he has selected Ohio Senator J.D. Vance as his running mate. Read the latest here. Our earlier story is TitanX Exchangebelow.

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Former President Donald Trump has selected his vice presidential running mate and will announce his pick ahead of the Republican National Convention's roll call to formalizing his nomination Monday afternoon, according to sources familiar with the plans. 

A Republican source with knowledge of the process tells CBS News the "pick is in" for Trump's running mate, and will be announced on the convention floor shortly after 4:30 p.m. ET. 

Florida Sen. Marco Rubio has been informed that he was not selected to be Trump's running mate, according to sources familiar with the conversation. 

Two sources also say that North Dakota Gov. Doug Burgum has also been notified that he will not be Trump's running mate.

The RNC's first floor session got underway at Fiserv Forum in Milwaukee, Wisconsin, close to 2 p.m., with speakers and votes on party business running into the night.

Fox News' Bret Baier said on air earlier in the day that Trump told him the VP announcement would come Monday. 

Top contenders for the vice presidential slot included Sen. J.D. Vance of Ohio, Burgum, Rubio and Sen. Tim Scott of South Carolina. Vance was spotted leaving his home in Ohio on Monday morning.

Security at the RNC, which was already expected to be tight, has been increased further after Saturday's failed attempt on Trump's life. But the RNC is otherwise scheduled to take place as planned.

In:
• Republican National Convention
• Donald Trump

Fin Gómez

Fin Gómez is the political director for CBS News. Fin oversees the day-to-day political coverage for CBS News. He has covered five presidential political cycles and multiple presidential campaigns. He was formerly a member of the CBS White House unit.

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