The showdown between Hillary Clinton and Donald Trump is Tuesday’s main focus, obviously, but not the only Big Question about what our national government will look like in January 2017. Democrats could regain a U.S. Senate majority, some polls and commentators suggest, although a number of the 34 races for that chamber are very tight.

The 100 senators (two from each state) serve six-year terms, with elections staggered so that about one-third of seats are filled every two years. Fifty-four senators now are Republicans, but the party faces tough challenges in Wisconsin, Illinois and Pennsylvania. Races in New Hampshire, North Carolina, Missouri and Indiana also are tight.

Republicans are defending 24 Senate seats this year. while Democrats defend 10. To control the Senate, Democrats must gain four more seats if Clinton is elected, or five if Trump prevails (because his vice-president would vote to break any deadlocks). At stake is the next president's ability to get policy proposals passed by Congress and to get nominees confirmed by the Senate -- which this year hasn't acted on a Supreme Court nominee to replace the late Justice Antonin Scalia, who died nine months ago.

Two states have Senate races where both candidates are women. Sen. Kelly Ayotte, R-N.H., faces a strong challenge from Democratic Gov. Maggie Hassan. In California, two Democratic women — Rep. Loretta Sanchez and state Attorney General Kamala Harris — are vying to replace Sen. Barbara Boxer, who’s retiring after 24 years in office. Reince Priebus, head of the Republican National Committee, predicts his party will keep at least a one-seat Senate edge. In the House, where all 365 seats will be filled Tuesday, Republicans brace for a loss of possibly a dozen seats -- but are seen as almost sure to keep a majority. Our system lets different parties control the White House and Congress, if that's what voters decide, as an example of "checks and balances" on government power.

Columnist says: "Thirty-four states have Senate races this year, but most of them involve incumbents so safe they could not be dislodged by a rocket launcher." – Gail Collins, The New York Times

Campaign veteran says: "If the presidential election narrows to less than 3 percent, then Democrats will need some good fortune to win control of the Senate. My advice is to watch the margin between Clinton and Trump." – Peter Hart, longtime Democratic pollster

Republican chairman says: "As of today [Nov. 4], we will hold the Senate, absolutely. . . . I think certainly 51 [seats] or more." – Reince Priebus, Republican National Committee chairman