Sunday: Fiorina expected on the main stage, Republicans take a pledge, and the feud between Donald Trump and Jeb Bush heats up

(CBS News) --It's been a week of big promises and small spats in the GOP contest for the 2016 presidential nomination.

The RNC, in a clear attempt to gain some control over the front runner Donald Trump, asked GOP candidates to pledge that they will not run as a third party candidate. Most signed the pledge, including Mr. Trump, who would not make such a promise during the first GOP debate.

Donald Trump also continued his attack on Jeb Bush this week for speaking in Spanish while criticizing his immigration proposals at a recent campaign stop. Trump said "he should really set the example by speaking English while in the United States."

And on the Democratic side, yet another batch of Hillary Clinton emails gave more insight into the personal life of the former Secretary of State. Plus, Joe Biden is polling third in Democratic field, leading to even more speculation around a possible presidential run.

The GOP also received new guidelines for the September 16th debate airing on CNN. The new rules allow any candidate who has polled in the top ten nationally from August 7th and September 10th, to appear on the main stage, which means GOP rising star Carly Fiorina is expected to graduate to the main debate stage. We'll ask Fiorina how she plans to stand out in a larger field this time and about the infighting in the Republican Party. And whether she trust Trump to keep his pledge to back the GOP nominee.

We'll also talk with Former Speaker of the House Newt Gingrichabout all the week's political news. As a 2012 presidential candidate, Gingrich is familiar with taking on the GOP establishment's favored candidate. We'll ask the former speaker about his views on the state of the 2016 race.

Plus, our annual Labor Day Book panel. This year, we talk to authors who've focused on historic innovators and inventors.

We hope you'll join us this Labor Day weekend. Check your local listings.