Washington (CNN) There's growing Democratic optimism for 2018. President Trump may have a new national security strategy. And Republicans brace for another intra-party feud over a southern Senate seat.

It's all in this week's "Inside Politics" forecast, where you get tomorrow's headlines today.

1. Why Dems' 2018 wave may be big

Recent election results, such as Doug Jones' win an Alabama, have Democrats thinking big. Just how big might surprise you.

It would take a swing of 24 seats to flip the House from Republican-controlled to Democrat -- no easy task given the way congressional districts are drawn these days.

And while Republicans will have just a 51-49 Senate majority once Alabama's Doug Jones is sworn in next year, the conventional wisdom for months has been that the Senate math favors the GOP because so many of the seats up in 2018 are held by Democrats, including 10 in states President Trump won in 2016.

But the 2017 election results, combined with high engagement among Democrats and a GOP suburban slump, have Democrats quite bullish.

Jonathan Martin of The New York Times shared his reporting about how some seasoned Democrats are thinking big.

"You hear the party talking about 40 seats now," Martin said Sunday on CNN's "Inside Politics." "It's a long way until next year's election, but you have people who are typically sober looking at a heck of a year next year in the House."

2. Will Trump's national security speech have a shelf life?

President Trump on Monday will deliver a speech in conjunction with his administration's release of its official national security strategy. It's the White House's chance to offer a roadmap about how the President and his team view the world and will respond to potential threats.

And the global challenges facing this President are many, from ISIS to North Korea to the China challenge and beyond.

So it will be a document and a speech that deserve attention. But will it have a long shelf life?

That question came up in the reporting of Politico's Eliana Johnson, who says Trump's frequent changes of heart raise questions about whether a position laid out this week will survive into next year -- or even next week.

"I'll be watching whether this document merely collects dust or whether it actually serves to guide the administration's foreign policy," Johnson said. "Up until now, it really seems to have been guided by the way the president wakes up feeling."

3. A Trump-Tillerson détente on North Korea?

North Korea's nuclear and missile programs top most lists of the most pressing national security challenges facing President Trump.

Meanwhile, there were new dustups this past week between Trump White House aides and Secretary of State Rex Tillerson.

CNN's Sara Murray reports that many in the Trump inner circle believe there will be some big North Korea decisions to make in the near future, perhaps even during the President's Christmas break in Florida.

And, despite all the media accounts of Trump-Tillerson tensions, Murray thinks there could be a year-end truce of sorts.

"I'm told by at least some that privately, they have reached a temporary détente," Murray said Sunday. "Now it's Trump, so temporary could be key here."

4. The tax bill's winners and losers

There is no question that corporations are the biggest winners in the tax-reform legislation due for votes this week in the House and Senate.

But what about other interests that were lobbying furiously to the end as negotiators tried to settle differences between the House and Senate versions?

If you've got student loan debt, you get to keep that deduction. Ditto for families with high medical costs: That deduction remains as well.

Bloomberg's Sahil Kapur tracked the tax bill horsetrading and says the final version does not include some provisions pushed by social conservatives.

"A tax break for unborn children that reproductive rights advocates feared would threaten legal abortion was defeated at the last minute," Kapur said.

5. Mississippi could be showcase for next GOP clash

Ailing Mississippi Sen. Thad Cochran's staff says he is expected back in the Senate this week for the big tax cut vote.

But the Republican leadership isn't ready to bet the bill on that, and worked late last week to get enough votes to pass the measure even if Cochran and Arizona's John McCain remain sidelined by health issues.

Cochran also missed time in the Senate earlier this year because of health problems, and there are quiet contingency conversations in both Mississippi and Washington about what would happen if Cochran is unable to return to work -- or if he decides to step aside in 2018.

Having those discussions might seem a tad crass, but Mississippi law is a factor. If the Senate is in session at the time the vacancy occurs, the state's governor must appoint an interim senator within 10 days.

Again, all this is in its relative infancy. But GOP sources with knowledge of the conversations say allies of Chris McDaniel, a tea party Republican who lost a fiercely contested primary to Cochran in 2014, believe he should be the leading candidate for for interim senator.

But the Republican establishment, which went on full alert to quash the McDaniel challenge in 2014, has zero interest in that.

As we just witnessed in Alabama, Majority Leader Mitch McConnell has a keen interest in keeping Republicans he views as agitators off of the ballot and out of the Senate. The GOP sources keeping track of the Mississippi whispering say the establishment favorite, should there be a Cochran vacancy, is former Gov. Haley Barbour, who is also a former Republican National Committee chairman and a veteran Washington lobbyist.

This is all theoretical at the moment, because Cochran's staff predicts he will be back to work soon. But here is another factor in the contingency planning: If a vacancy happened in 2018, state law calls for a special Senate election to coincide with the normal election that year, which would mean both of Mississippi's Senate seats would be on the ballot.

McDaniel has already talked of maybe mounting a primary challenge against incumbent GOP Sen. Roger Wicker. If both seats were on the ballot, the 2014 Cochran race and the more recent Alabama race would serve notice that the Magnolia State could become a giant stage for the festering GOP faction wars.