Emily Bazelon, David Plotz, and John Dickerson discuss the newly launched presidential campaigns of Democratic candidate Hillary Clinton and Republican contender Marco Rubio. They also talk about the recent action by Congress over the Obama administration's nuclear deal with Iran.     Twitter: @SlateGabfest Facebook: facebook.com/Gabfest Email: gabfest@slate.com Show notes at slate.com/gabfest     This week's episode is sponsored by Stamps.com. If you go to stamps.com, click on the microphone at the top of the home page and enter GABFEST for a $110 bonus offer, including up to $55 in free postage and a no-risk trial. This week's episode is also sponsored by the University of California, committed to creating solutions to today’s environmental challenges. To uncover groundbreaking research from the University of California, visit slate.com/breakthroughs.   Join Slate Plus! Members get bonus segments, exclusive member-only podcasts, and more. Sign up for a free trial today at www.slate.com/gabfestplus. Learn more about your ad choices. Visit megaphone.fm/adchoices