After reports surfaced Tuesday, Arizona Republican Sen. Jeff Flake took to the Senate floor to announce he will not seek re-election in 2018.

Flake said early in his nearly 20-minute speech, "There are times when we must risk our careers in favor of our principle. Now is such a time."

But why is now the time?

The simplest answer may be that Flake does not think he can win the 2018 Senate race.

As the junior senator is coming to the end of his first 6-year term, recent poll numbers show Flake is only 25 percent favorable to Arizona voters. The same poll, released last month, also predicted that opponent Kelli Ward would have beat Flake in the primary.

Not only is Ward polling high among Arizona voters, she already received a blessing from President Donald Trump's former right-hand man Steve Bannon.

And Ward may have Trump backing her, whereas Flake and Trump have a long-running battle. Flake's speech Tuesday just added to the fire. It's possible Flake saw he could not compete with those two Republican powerhouses behind his opponent.

Flake has been a loud voice in Congress when it comes to criticizing Trump. In July, he released a book in which he called out the president and his party as a whole for enabling Trump. His announcement to step back from re-election echoed those same sentiments.

"Reckless, outrageous, and undignified behavior has become excused and countenanced as 'telling it like it is,' when it is actually just reckless, outrageous, and undignified," Flake said Tuesday. "And when such behavior emanates from the top of our government, it is something else: It is dangerous to a democracy."

READ: Sen. Jeff Flake's full statement about why he won't seek re-election

The senator made clear Tuesday in his speech, he does not approve of Trump’s behavior, which puts him out of line with the GOP, Trump supporters and especially Trump supporters in Arizona.

And while the announcement came Tuesday, Flake still has more than a year left in his term. Flake proved he can no longer stomach Trump, but his track record shows he may still vote with Trump for the remainder of his time in the Senate. The Arizona conservative votes with Trump nearly 90 percent of the time, including on the proposed repeals of the Affordable Care Act.

So, with Flake out, who will take his seat?

While polls show Ward is favorable among Republican voters, it is too early to tell who will be elected senator in 2018.

Just a few weeks ago, Democratic Congresswoman Kyrsten Sinema announced she is entering the Senate race.

Additionally, Republican Rep. David Schweikert, former Arizona Republican Party Chairman Robert Graham and Congressman Trent Franks have all been rumored to make a run at the seat.

What was expected to be a two-person race could now have many opponents.