This story was originally published on nationaljournal.com on March 21, 2016. 

With a con­tested Re­pub­lic­an Na­tion­al Con­ven­tion as the most likely out­come this un­likely primary sea­son, Re­pub­lic­ans are try­ing to cal­cu­late what it would mean to have Don­ald Trump at the top of their tick­et. Polling at this point shows Hil­lary Clin­ton trail­ing John Kasich by an av­er­age of 7.4 points, Marco Ru­bio by four points, and ef­fect­ively tied with Ted Cruz. But Clin­ton beats Trump by 6.3 per­cent­age points. A good case can be made that Trump is pos­sibly the only Re­pub­lic­an who can’t beat Clin­ton.

Con­sider the ef­fect on GOP Sen­ate and House ma­jor­it­ies. A Trump-led tick­et would be dis­or­i­ent­ing for Re­pub­lic­ans. Just as the Demo­crat­ic Party has been trend­ing more lib­er­al since Pres­id­ent Bill Clin­ton left of­fice 15 years ago, the Re­pub­lic­an Party has been mov­ing to the right just since Pres­id­ent George W. Bush left of­fice just over sev­en years ago. Not long ago, many con­ser­vat­ive Demo­crats in Con­gress were fur­ther to the right than many lib­er­al Re­pub­lic­ans. But that ideo­lo­gic­al over­lap has dis­ap­peared. Each of the two parties has be­come com­pletely ideo­lo­gic­ally co­hes­ive.

Giv­en the stead­ily right­ward move­ment in the GOP, tak­ing a 90-de­gree turn to­ward Trump is hard to fathom. Trump-ism is based on an­ger, which is an emo­tion, not an ideo­logy. If Trump has an un­der­ly­ing ideo­logy, he’s keep­ing it to him­self. Giv­en con­ser­vat­ive com­plaints that the last two GOP pres­id­en­tial nom­in­ees, John Mc­Cain and Mitt Rom­ney, were not con­ser­vat­ive enough, and sim­il­ar fights over wheth­er then-House Speak­er John Boehner and cur­rent Speak­er Paul Ry­an were suf­fi­ciently hard-line, the pres­ence of Trump at the top of the tick­et would be a head-scratch­er. At a time when ideo­logy is be­com­ing more im­port­ant, Re­pub­lic­ans would be put­ting their chips on an­ger. That’s a risky bet.

The Re­pub­lic­an Sen­ate ma­jor­ity is tenu­ous even if the GOP un­der­per­forms even a little on Elec­tion Day, even without a dis­rupt­ive can­did­ate at the top of the tick­et. With the GOP ma­jor­ity at 54 to 46, Demo­crats need a four-seat net gain if they hold the White House (the new vice pres­id­ent would break the tie), five seats if they don’t.

The Sen­ate works on six-year cycles, so this would be the re­bound elec­tion from the GOP’s ban­ner year of 2010. Twenty-four Re­pub­lic­an seats are in play, com­pared to only 10 for Demo­crats. More im­port­ant, Re­pub­lic­ans have sev­en seats be­ing con­tested in states that Pres­id­ent Obama car­ried in 2012, while there are no Demo­crat­ic seats up in Rom­ney states. One of those sev­en GOP-held seats in the Obama states is that of Sen. Chuck Grass­ley in Iowa, who just drew a cred­ible op­pon­ent. But even if Grass­ley holds on, Re­pub­lic­ans have six seats at risk. Sens. Mark Kirk in Illinois and Ron John­son in Wis­con­sin are both in ex­treme danger. They were able to float with the Re­pub­lic­an tide in a midterm elec­tion, but now they’re run­ning in a pres­id­en­tial year in very Demo­crat­ic states. Hard fights loom for Sens. Rob Port­man in Ohio, Pat Toomey in Pennsylvania, and Kelly Ayotte in New Hamp­shire, as well as Sen. Marco Ru­bio’s open seat in Flor­ida. Con­versely, there is only one Demo­crat­ic seat that’s a toss-up—Minor­ity Lead­er Harry Re­id’s open seat in Nevada.

Of these sev­en com­pet­it­ive Sen­ate races, four are in some of the very closest pres­id­en­tial states—Flor­ida, Nevada, New Hamp­shire, and Ohio. Loud foot­steps up­stairs in the pres­id­en­tial race could eas­ily shake the Sen­ate races be­low. If Re­pub­lic­ans were to lose the pres­id­ency by a mar­gin wider than Mc­Cain’s loss in 2008 and Rom­ney’s de­feat in 2012, hanging onto the Sen­ate would be a long shot at best.

The House is no longer par­tic­u­larly sens­it­ive to small-to-mod­er­ate shifts in the polit­ic­al winds. In­cum­bents are pro­tec­ted by nat­ur­al pop­u­la­tion pat­terns—Demo­crat­ic voters con­cen­trated in urb­an areas, close-in sub­urbs, and col­lege towns, and Re­pub­lic­ans in small-town, rur­al Amer­ica, and out­er-ring sub­urbs—by the polit­ic­al ger­ry­man­der­ing pur­sued by both parties for gen­er­a­tions. Demo­crats need a 30-seat net gain to cap­ture a House ma­jor­ity, a par­tic­u­larly tall or­der giv­en the cur­rent dis­tri­bu­tion of seats and the way dis­trict lines are drawn.

Cook Polit­ic­al Re­port House Ed­it­or Dav­id Wasser­man has writ­ten in re­cent days that it is now pos­sible that the GOP House ma­jor­ity could be in danger. A far more plaus­ible scen­ario, as­sum­ing the GOP pres­id­en­tial tick­et is weak, would be a loss of a dozen or more seats for Re­pub­lic­ans, cut­ting their House mar­gin in half. Giv­en the GOP’s dif­fi­culty in push­ing through le­gis­la­tion even with the largest House ma­jor­ity since 1928, Paul Ry­an will have a dev­il of a time win­ning votes if he loses this cush­ion.

All of this is why it is so in­ter­est­ing to see so many con­gres­sion­al Re­pub­lic­ans sit­ting on the side­lines of this po­ten­tially pivotal GOP nom­in­a­tion con­test. If the hard-core con­ser­vat­ives in the Free­dom Caucus mem­bers con­sider Ry­an and Boehner squishy mod­er­ates, what will they think of Trump, whose ideo­lo­gic­al roots are so shal­low that they don’t even add up to a polit­ic­al philo­sophy?