(CNN) —Florida Sen. Marco Rubio will seek re-election to the Senate, a boost for Republicans facing a tough fight to maintain their Senate majority in November.

Rubio is set to announce his plans later Wednesday, according to a source with knowledge of his plans. The decision follows a month of heavy lobbying from top Republicans and soul-searching on the part of Rubio after the Orlando attack.

Rubio's announcement marks a 180-degree turn from where he was even just a month ago, when he insisted he would give up his Senate seat at the end of this term.

Many Republican colleagues encouraged him to run, believing he's the party's best chance to keep the seat,

But not every Republican in the highly competitive Florida Senate primary was happy about the decision. Tea party favorite Ron DeSantis waved off questions about Rubio from a CNN reporter as he left a Capitol Hill meeting Wednesday morning.

Leading Democrats have already painted a bright target on Rubio -- Montana Democrat Jon Tester, leader of the Senate Democrats' campaign arm, said last week that beating Rubio could potentially kill any chances he has for the White House in 2020.

And the vicious Republican primary -- which Rubio exited only a few months ago -- is sure to be milled for attacks against Rubio.

Rep. Patrick Murphy, a favorite among establishment Democrats for the seat, quickly blasted Rubio on Twitter for missing numerous key Senate votes and intelligence briefings to campaign for the White House.

"Marco Rubio abandoned Florida. Unlike Rubio, I love working hard every single day for the people of Florida. ‪#flsen," Murphy tweeted, shortly after news leaked that Rubio was running again.