That is patently false. They will almost certainly keep the House. But the Senate is another matter.
There are 34 seats up for vote, 2/3 of them being GOP seats (They won a ton of seats 6 years ago after the Democrats voted Obamacare into effect).
The GOP has a 4 vote majority in the Senate now. But ignoring the seats that are basically locked in, the GOP has a 3 vote lead, 47 to 44. That leaves That leaves nine seats that are too close to call - Colorado, Nevada, Florida, New Hampshire, Pennslyvania, North Carolina, Ohio, Wisconsin and Illinois.
Obama won all of those states except for North Carolina. Worse, the GOP has a crisis of faith right now with 'outsider' candidates meaning the GOP can NOT get the assured turnout. Assuming Hillary wins, the well known effect of the president increasing senate and congress wins, It is likely that the Democrats will win at least 6 out of the 9 senate races in doubt. That puts them in charge of the senate again.
Granted, 2 years from now in the mid year election, that is likely to revert back to the GOP.