President Donald Trump on Friday said he wants to tackle infrastructure next – and he wants Democrats' help.

"At some point, and for the good of the country, I predict we will start working with the Democrats in a Bipartisan fashion," he tweeted Friday. "Infrastructure would be a perfect place to start. After having foolishly spent $7 trillion in the Middle East, it is time to start rebuilding our country!"

The administration signaled plans to roll out its infrastructure plan in January earlier this month. And Trump touted the yet-to-be rolled out plan following the Amtrak train crash in Washington state this week.

"The train accident that just occurred in DuPont, WA shows more than ever why our soon to be submitted infrastructure plan must be approved quickly," he wrote Monday. "Seven trillion dollars spent in the Middle East while our roads, bridges, tunnels, railways (and more) crumble! Not for long!"

During the 2016 campaign, Trump promised to introduce a $1 trillion infrastructure plan in his first 100 days. That never came to pass; instead the focus was primarily on multiple immigration orders, failed attempts to repeal Obamacare and, ultimately, last week's successful plan for a $1.5 trillion tax cut.

The window to tackle major issues in the new year is small. While lawmakers are typically wary of tackling tough policy fights in election years, Republicans are mindful that their Senate majority is shrinking by at least one seat, when Alabama Democrat Doug Jones is sworn in to replace Republican Luther Strange, amid predictions of a coming Democratic wave that threatens their majority in the House as well.

Senate Majority Leader Mitch McConnell, R-Ky., acknowledged that reality this week when he cast doubt on House Speaker Paul Ryan's suggestion that the GOP would take up welfare reform as their major legislative priority in 2018.

"I think the Democrats will not be interested in entitlement reform, so I would not expect to see that on the agenda. And what the Democrats are willing to do is important," he said Wednesday. "Because, in the Senate, with rare exceptions like the tax bill, we have to have Democratic involvement."