Can the Democrats take the Senate? A senior official speaks of the brutally difficult way.

If Democrats can hope to gain control of the Senate, they have to overcome a very difficult math problem.

At present, even though it seems that Democratic incumbents in countries like Ohio, Pennsylvania and Wisconsin will probably survive, four of them – Bill Nelson in Florida , Heidi Heitkamp in North Dakota, Claire McCaskill in Missouri and Joe Donnelly in Indiana – locked in extremely difficult races.

Here is the friction. Democrats must keep all these seats and two net GOP seats up of that – probably in Nevada and Arizona, which are also very close – from 49 to 51 seats and win the Senate. If any of these four Democrat holders loses, the Democrats must overthrow three GOP seats, which is very difficult. If two of them lose, the Democrats must overthrow four GOP seats, which is really very unlikely.

In other words, it is hard enough for Democrats to turn to Arizona and Nevada – but at every seat they lose, Democrats must increase their net number of seats for Republicans. It's discouraging.

Today, I spoke to J.B. Poersch, Senate Chairman Majority PAC, the biggest spending super PAC to elect Democrats in the Senate. He acknowledged that the situation was "difficult".

"We have a long way to go," conceded Poersch. "But I do not think the Republicans were waiting to play the goal-line defense as they are."

This basic mathematical problem is partly due to the fact that Nelson – the only one of the four incumbents in a state that Barack Obama has won twice – is participating in a much tighter race in Florida than many were hoping against GOP governor Rick Scott .

When I urged Poersch about it, noting that many Democrats think Nelson is running a dull campaign, he refused to admit that Nelson is struggling. Instead, he said the Democrats should have always expected the race to be tight. "We are running against an eight-year-old governor with all the financial resources in the world," Poersch said. "Of course it's going to be near."

In all fairness, even if the situation is difficult for Democrats, it seems worse for Republicans than most people expected. After all, the card favors Republicans because many Democrat holders are defending in the states that President Trump has worn. However, there are plausible paths, even if they are very narrow, to the Democratic majority.

Poersch argued, for example, that Tennessee – where Democrat Phil Bredesen is launching a surprisingly strong challenge – is more at stake than many people think.

"Republicans are doing 16 consecutive weeks of television and radio there," Poersch said. "They did not plan to go so far and so far to Tennessee. … We believe that we have held our heads here for a while. "

The thing is that Tennessee looks like a must win for Democrats if they want to win the majority. It goes back to this mathematical problem again: If a practicing democrat loses in any of these four states, the democrats duty topple Tennessee in addition to Arizona and Nevada to win the Senate. The only alternative is to spin the table in all six states other than Tennessee.

So, Tennessee is probably crucial. When I asked this question to Poersch, he said, "It is possible to reach the majority without Tennessee. But it's a priority.

What about Texas?

Which brings us to Texas, where Beto O'Rourke launches a surprising challenge to Ted Cruz. When I asked Poersch if his group was going to invest in the race, he objected, saying only: "We are looking at it closely" and "we reserve the right to help", although he has described O'Rourke as "the best Democratic candidate in Texas for 25 years. "

This raises a dilemma. Given the ease with which a Democratic majority can be baffled by a single loss somewhere – and given that in this political environment anything can happen, as we saw in Alabama – national democrats could invest in Texas a miracle. With this in mind, Democrats could also consider investing in Mississippi, where the Democrat Mike Espy could draw a shock. As this is a "primary jungle" multi-candidate election day, if no one reaches 50% and that Espy ranks among the top two, this would result in a second round at the end of November .

And if the Democrats do not invest in Texas (or Mississippi) – and O'Rourke (or Espy) falls right next door, and the Democrats fall one short of the majority – the recriminations will be extreme. When asked about this, Poersch acknowledged the difficulty of the situation. "In a cycle with a card as wide as that, you have to give yourself a lot of possibilities," he said. As to whether this translates into national spending in Texas, well, we'll just have to wait and see.